This blog is translated from German with DeepL.
Our entry
In cooperation with the company CELLWAR GmbH from Münchenbuchsee, we have realized a flexible robot cell in which plastic parts are joined together with laser light.
The process
The welding of plastics with laser is fundamentally different from the (arc) welding of metal. There is no molten pool, there is no need for additional welding material, and there are no welding beads. In fact, the product looks the same as it did before welding, yet a high-strength joint is created.
In plastic laser welding, actually more accurately referred to as through-welding, the laser beam penetrates one laser-transparent plastic component and is absorbed at the boundary to the second component (laser-absorbing material). Due to the necessary contact pressure, the heat in the absorption zone is conducted into both components until the polymer chains interlock. After cooling, the parts are firmly connected to each other.
graphical representation of the joining principle
Consequence of this joining principle: Basically, you cannot join two identical materials because one must be laser-transparent, the other laser-absorbent. The diagram below should be understood as a rough guideline, but should not be regarded as absolute, because depending on the plastic additives, the laser absorption is greater or smaller. However, for special applications, laser welding between identical or barely weldable plastics can be made possible with additional additives.
If you are a bulk buyer of plastics, you can have your own ideal plastic mixed. If you do not have the possibilities or the familiarity to do this, our experience shows that you can hardly avoid an effective practical trial with appropriate tests.
The entire heating, pressing, fixing and cooling process is a continuous process that can only be realized reliably with one machine. If the material, the laser intensity, the contact pressure or the path speed of the laser head are not coordinated, the desired or expected result will not come out.
The surface that is penetrated by the laser and pressed on by the laser head is intact and suitable for optically demanding components.
Experience
Gimelli Engineering AG supported CELLWAR GmbH in the planning, installation, commissioning, training and documentation for the laser welding system. Furthermore, the robot programming including the control of the interfaces was carried out.
Within a very short time, CELLWAR GmbH was able to weld the required plastic products in different variants reliably and with high quality using the system. The weld seams achieved are of such good quality that they can hardly be separated even above the product specification. The breaking point in case of excessive load is next to the weld seam.
Despite the automation, the production of the product family does not require less manpower, because it is not a fully automated production line, but all the more a flexible and adaptable solution. The robot system takes over the precise task of the welding process and the production capacity could be increased. The feeding of material to the production island and the supervision of it is deliberately still in human hands.
Possibilities
Depending on the geometry or shape, products can basically be processed on the system up to an area of approx. 3m2 (flat products). In the case of curved or shaped products, this can also be much more. It therefore depends on how the component can be positioned relative to the articulated arm robot – deflection radius approx. 1.6m. The flexibility of the system allows products to be welded at short notice, from batch sizes of one to practical trials for future products and material combinations. The accessibility of the laser head, in combination with the degrees of freedom of the robot, must always be taken into consideration.
CELLWAR GmbH or Gimelli Engineering AG will be pleased to advise you in the development as well as in the production of laser-welded plastic products.
Conclusion
We see the advantage of laser welding compared to ultrasonic, infrared or hot plate welding of plastics in its flexibility. No product-specific, energy-transferring tools, such as sonotrodes or heating tools, are required. This comes into its own particularly in the case of small quantities and short delivery times.
Due to the flexible degrees of freedom of the jointed-arm robot, free-form surfaces can also be processed. And as already mentioned, the result is a perfect joining of the plastics.
