Laser Marking for Metal
This section describes information ranging from the principles of metal marking and processing to advantages grouped by laser wavelength.
It introduces marking examples and the optimal laser markers for a variety of materials such as aluminium, stainless steel, iron, copper, cemented carbide, and gold plating.
- Metal marking types
- Metal processing types
- Absorption rate for metals
- Aluminium
- Stainless steel / Iron
- Cemented carbide
- Copper
- Gold plating
Metal marking types
Black-annealed (oxidation) marking
When the laser beam is applied to the marking target, the focus is shifted so that only the heat will be conducted. Applying heat without engraving the target forms an oxide film on the surface. This film appears black and represents black marking.
White etching marking
The laser beam is applied to the marking target at the focal point. The metal surface is slightly removed to expose an uneven surface. This cause irregular reflection of light to create marking that appears white.
Engraving marking
Laser light irradiates the focal point and etches the surface of the target for marking. A deeply engraved impression can be made by increasing the amount of engraving by increasing the laser irradiation count.
Surface peeling
Uses laser irradiation to peel off the surface and remove the electroplating of the target for marking. This makes the substrate visible, and brings the marking into view.
Metal processing types
Laser cutting
Focuses the laser light output by a laser oscillator and irradiates any fixed point from the irradiation unit to melt the target. Because there is no contact, it does not cause a reaction with the item processed. Deformation and cracking is kept to a minimum. In addition, because it is possible to specify processing areas in extreme detail, it is possible to create localised holes or cuts in places where cutting tools cannot fit.
Solder barrier
Due to the trend toward smaller and thinner, some connector terminals have solder barriers (nickel barriers) to control solder from soaking up. Conventionally, masking was used on locations where electroplating is not necessary, but removing the mask material took time and effort. Surface peeling using laser light is effective in these cases.
Welding
Laser welding is a method that irradiates laser light on targets and joins them at a location by melting and solidifying the metal. It is possible to irradiate a pinpoint with high density energy and complete the process at high speeds. Material distortion due to heat can be kept to a minimum. In the past, deformation occurred easily. Now even thin materials can be welded.
Soldering
The heat from the laser melts the solder paste and joins the metal.
Irradiation of localised laser spots is possible, so irradiation is suitable for small parts. In addition, compared to the flow method where heat is added to the entire part, it is possible to reduce the load caused by the effect of heat on the part.
Absorption rate for metals
The graph below shows the different absorption rates of metal materials with a green laser (532 nm) and with the standard wavelength (1064 nm). There is no significant change to the absorption rate for iron (Fe), nickel (Ni) or aluminium (Al) when the wavelength is changed. However, the absorption rate for gold (Au) and copper (Cu) is affected greatly by changes in wavelength. The absorption rate for gold (Au) with wavelengths of 532 nm is approximately 30%, but with the standard wavelength of 1064 nm the absorption rate is less than 10%. Similarly, with a wavelength of 532 nm, copper (Cu) has an absorption rate of 40%, whereas that rate is less than 10% with the standard wavelength of 1064 nm.
Aluminium
Black-annealed Marking
On aluminium surfaces, black-annealed marking appears as a highly visible dark grey. Heat is applied to the metallic surface with a laser, which makes the marking a dark grey.
- Selection factor
- Aluminium has a higher reflectance than iron or stainless steel, so select a laser with a high peak power. For aluminum materials, laser markers with the standard wavelength (1064 nm) are optimal. Keep the beam spot diameter small and mark with a high energy density where the laser beam is in focus to achieve beautifully coloured marking.
- Recommended model
- MD-X Series Hybrid Laser Marker
White Marking
White marking is achieved by lightly engraving the surface of the material.
Roughing the metal surface causes a diffuse reflection of light, resulting in white marking.
- Selection factor
- Increasing the power and setting a faster scan speed allows users to perform white marking stably and under a wide range of conditions. As with black-annealed marking, laser markers with the standard wavelength are optimal.
- Recommended model
- MD-X Series Hybrid Laser Marker
Stainless steel / Iron
Black-annealed Marking
Oxidising the surface using heat allows for more vivid black marking. Engraving/embossing is possible at 1 μm or less, thus minimising damage to precision metal components.
- Selection factor
- Laser markers with the standard wavelength are optimal. Defocusing allows for a reduced energy density, thus providing black marking without the need for engraving. Using a high-output laser marker allows marking to be performed at a higher speed.
- Recommended model
- MD-X Series Hybrid Laser Marker
White Marking
White marking is achieved by lightly engraving the surface of the material.
Roughing the metal surface causes a diffuse reflection of light, resulting in white marking.
- Selection factor
- Increasing the power and setting a faster scan speed allows users to perform white marking stably and under a wide range of conditions. As with black-annealed marking, laser markers with the standard wavelength are optimal.
- Recommended model
- MD-X Series Hybrid Laser Marker
Cemented carbide
Black-annealed Marking
Black marking is possible with no embossing just as with aluminium, stainless steel, and iron.
- Selection factor
- In order to avoid cracking super-hard materials such as tools, fine adjustment of the Q-switch frequency is essential. Hybrid laser markers capable of producing a high peak power and short pulse lasers are best.
- Recommended model
- MD-X Series Hybrid Laser Marker
White Marking
White marking is achieved by lightly engraving the surface of the material.
Roughing the metal surface causes a diffuse reflection of light, resulting in white marking.
- Selection factor
- Increasing the power and setting a faster scan speed allows users to perform white marking stably and under a wide range of conditions. As with black-annealed marking, laser markers with the standard wavelength are optimal.
- Recommended model
- MD-X Series Hybrid Laser Marker
Copper
Surface peeling
White marking is achieved by lightly engraving the surface of the copper material, allowing for a white finish.
- Selection factor
- Copper has a high reflectance, so select a laser with a high peak power. UV lasers will have a higher absorption rate with metal compared with the standard wavelength, allowing for shortened marking takt times and reduced damage to the target. Marking will be possible with standard wavelength lasers, but the lower absorption rate means marking will take longer, leading to soot and the like being generated at the marking location.
Gold plating
Surface peeling
White marking is achieved by lightly engraving the surface of the gold plating, allowing for a white finish.
- Selection factor
- Adjustment of the Q-switch frequency is required. In addition, thicker plating layers will make marking more difficult and require longer marking times. UV lasers offer a higher absorption rate and do not apply excess heat, making it possible to obtain a high-quality finish.
