On the way to the digital factory: Flexible marking of injection molded components with the laser
In injection molding, marking standards are a widespread solution for inserting the material identification, the production date resolved to the year and month, into the injection molded part. In addition to the acquisition costs, the standards also cause additional costs in production and make the injection mold itself more expensive.
In the age of industrial digitalization and the circular economy to increase sustainability, this common approach is an anachronism. The fully digital and contact-free marking of injection molded components using lasers offers enormous potential here, which will be explained below.
Recalls by car manufacturers are not uncommon these days and the associated costs and damage to image are enormous. With production outputs of several thousand vehicles per day, it is clear that time stamps with monthly resolutions are not an option. Rather, it is desirable to be able to look at production to the second so that damage can be precisely localized in the event of a problem. Other information such as material batch, production machine and operator are at least as relevant and can also be linked to customer information.
But it doesn't have to be a disaster to recognize the benefits of flexible digital solutions. If you look at the packaging industry and its recycling processes, you realize that a lot of packaging is multi-layered and made up of various materials. Packaging is becoming increasingly complex, and here too - for food or pharmaceutical applications, for example - the information content and therefore the traceability of the packaging can be significantly improved.
If product identification is combined with upstream quality control, the marking can be accompanied by a good/bad part identifier, thus automatically avoiding the use of poorly rated parts. A step that can be linked to the verification of the applied code.
To stay with the automotive example: Here it is not uncommon to subsequently apply additional product information using adhesive labels. A process that requires additional work steps and logistics and has the drawback that these labels can be damaged or lost - i.e. they are not necessarily permanent. This is not the case with laser marking, which incorporates the information content into the molded body and is therefore just as permanent as the material from which the injection moulded components are made. In addition, laser marking represents a significantly higher hurdle against product counterfeiting.
As laser marking is an additional process step compared to the use of standard parts, the question of integration and cost-effectiveness arises. There are several conceptual approaches.
One elegant option is to also use the laser marker to separate the sprue and thus complete the marking and separation of the components in just one operation.CO2 laser sources with 10.6 µm radiation in the infrared (IR) range are used for this, as material has to be vaporized for the separation cut. The cut edge can be produced in very high quality for most materials and there is no need for post-processing. The marking is then typically an engraving, with the exception of a few materials.
In the exceptions - such as PVC - a color change occurs, as is also known from marking with fiber lasers in the near infrared range (NIR).
Fiber lasers are successfully used for product marking in both aluminium die casting and plastic injection moulding. While the material interaction with metals ranges from annealing marking (color change of the metal due to heating) to engraving, the desired result in the plastics sector is the aforementioned color changes. Many plastics, such as filled or unfilled products from the PA or PP families, react automatically to laser radiation in the NIR. However, the effect can be enhanced by adding additives and, for example, produce pure white marking on black PA66. A high contrast ratio is required for machine-readability. Additives have now reached the point where markings in other colors are also possible and there is also a free choice of colors for the molded parts.
If the marking process was previously defined as an additional process step, considerable savings can be made across the entire process chain - if laser marking permanently replaces labels and standard parts. In the digitally controlled production process, sources of error such as incorrectly positioned date arrows and the entire effort for the standard parts in mold making itself then disappear. The information of the marking by color change can be displayed as human readable text and with the usual symbols, but also as a data matrix code. In each individual case, it is important to consider how much information and what type, size and cycle time of the marking is appropriate. This decision can be reversed at any time and adapted to new conditions. Maximum flexibility in production with increased transparency in the product life cycle meet the requirements of customers and legislation in an equally efficient and cost-conscious manner.
The fact that industrial laser technology, which has now been available for 60 years, is constantly evolving and opening new doors can be seen in the annual increase in sales figures. In addition to laser-based deburring of injection molded components, the applications described are another useful area of application for introducing more sustainability into the plastics processing industry and at the same time increasing the competitiveness of individual suppliers.
