The term laser marking is a generic description used to describe the broad range of surface changes (“the mark”) that can be achieved when the laser energy is applied to the very extensive range of materials used in industry today. The laser process generates visual contrast between the processed element and the background.
In the following paragraphs we will explain when, where and how these occur and how you select the best combination for your material requirements.
Surface changes such melting, ablation, foaming, molecular, chemical and colour can occur depending on material selection and laser source used. The process of laser marking relies on the material absorbing laser light, rather than a mechanical type impact, and converting it into thermal energy. This provides many benefits but is also the reason why so many variations of mark types can be achieved.
In the case of metals the two traditional process results are fairly straight forward. Heating the surface until it reaches vaporisation temperature results in an engraved mark, sometimes referred to as ablation. The depth to which the engraving occurs is dependent on material and parameters used (power, speed and pulse rate). The second method is referred to as Annealing or CW marking. With this process the material never gets to vaporisation temperature so no material is removed. Instead the heating effect causes an oxidation process beneath the material surface creating a permanent dark mark which effectively has depth and so becomes permanent rather than a surface mark. In both cases the process is very fast (energy density) and localised (spot size) so very little, or no, damage is caused to the materials away from the mark area.
Most plastics, when exposed to laser energy will have a thermochemical reaction. The kind of reaction is dependent on the material and the wavelength of laser used. Material manufacture, surface finish and colour all can play a part in the resulting mark. Some of the more common reactions can be described as melting, foaming and colour change.
When CO2 is used on plastics the most common resulting mark is Melting. The plastic absorbs the energy very quickly resulting in the material melting rather than vaporising. The results tend not to create a contrast to the surface as any residue material simply reflow and return to solid a state.
When fibre or Yag lasers are utilised some plastics will react by generating gas bubbles to the material surface as a direct result of heating from the laser energy. Referred to as foaming the resulting effect changes the specular reflection values creating a visible contrast.
Colour change can occur in two main ways. Bleaching occurs when the pigment or additive is removed during the marking process. The pigment acts as the absorption barrier reacting to the laser energy at a higher level to the core material. The chemical response is the removal of the pigment. When bleaching occurs the change tends to result in a lighter mark to the original. Because the reaction takes place below the surface the mark suggests no disruption to the surface. In the second process the surface of the polymer is disrupted, by the transfer of light energy into thermal energy, releasing carbons to the surface, Carbonisation. This is most effective on lighter coloured plastics and organic materials as the process produces contrast levels that can be described as light grey to black.
Commercially available laser additives are now used in many plastic materials to introduce more effective process parameters. These additives change the energy absorption properties allowing higher levels of contrast to be created, better edge definition along with faster processing speeds.
One further process additive is available. In this instance the additive is applied to the surface rather that included in the master batch. Thermark is a product that is used to enhance marking as well. The product can be used on metals, ceramics, glass and other hard surfaces, creating a high contrast mark where it may not be achieved without an interim material. The laser heats the Thermark in order to fuse the material (a ceramic glaze) to the host material surface. It is the pigments used within the chemical mix (Thermark) that provides the high levels of contrast. The non-fused material is removed easily with a light washing process is used.
Explain just how flexible laser marking can be for me
Laser marking processes can satisfy almost all permanent marking requirements. From part identification and traceability, to corporate promotion, the versatility of laser marking has the power to meet your needs. When you consider that the process does not involve contact or impact onto the component, no chemicals are used and very rarely are additional processes required (drying, curing or bonding) then laser marking ticks all the boxes.
Today most laser marking equipment will be supplied with software that allows you to create and configure all your mark data requirements. Effectively a desk top publishing programme that will contain all the necessary tools to generate data such as alphanumeric characters including sequential marking to tools for the importing of technical images and artwork. A full list of laser and its software capabilities are described further down on this page. Images are also provided for each description.