JOINING | INNOVATION
eMotion servo-driven system with a pneumatic drive system (using high-cost compressed air), in which the eMotion system showed energy savings of 87% as well as a faster cycle time, improved finished part strength and aesthetic improve- ments. The two systems were identical in frequen- cy, power, and stroke, while only the drives differed. “We expected the electrically driven ultrasonic welding machine to perform better in terms of energy consumption, but we didn’t expect such a big difference,” says Jürgen Baumert, Head of R&D at Rinco. The company is continuing to examine the benefits resulting from servo motion control technology in the ultrasonic welding process. It admits that “servo drive technology is not the answer to every application in ultrasonics, it shows promise for customers focused on energy savings and assembly quality in plastic part assembly”. Herrmann Ultraschalltechnik, the German specialist in ultrasound welding technology, revealed it has done testing work on welding recycled plastics in an interview with VDMA Plastics and Rubber Machinery Association in Germany. Jochen Ochs, Head of Application Technology Plastics at Herrmann Ultraschalltechnik, discussed the findings as part of VDMA’s Way2K industry interviews in the lead-up to the K 2022 trade fair. Ochs said: “Whether and how well 100%
recyclates can be welded depends on the material in question. It is difficult to make a general state- ment because each recyclate is different and multiple melting can have a negative effect on the material properties. We had test specimens made from a regranulate for our laboratory and found that we could use them to produce very good welded joints. In principle, we are therefore able to weld 100% percent recyclate with ultrasound.” The company undertook the test work to find
out if ultrasound welding of recyclates would have particular problems. “Before we receive a customer request to use recyclate, we wanted to know what we were up against. Now we have to see how the market develops and what kind of requests will actually be made to us in the future,” said Ochs. In the testing, a standard polyamide was
compared with a high-quality recycled PA. Project partner Barlog produce test specimens from the recycled PA, which was compared with the stand- ard PA test specimens. Herrmann set up a statistical design of experiments (DoE) with 18 different parameter groups. It then tested tensile samples and compared them. Ochs said: “We created cross-section views after
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each welding process. Initially, it became apparent that the recyclate looked rather worse in the cross section. A parting plane could be seen between the upper and lower parts. The standard material initially showed a much more homogeneous weld, with no parting planes visible in the sectional view – the part looks as if it were made from a single cast. In preliminary tests, we found a parameter set that was suitable for both materials as initial parameter. We then created a DoE for this parameter set and welded five parts each with different parameter configurations. Finally, we obtained comparable results in the tensile test for both material types. In fact, we had expected the recyclate to get worse results, both in the cross-sectional view and for the tensile test. But there was a parameter set with which equally good results could be obtained.” He indicated the necessity of doing tests on
recyclate batches due to a lack of knowledge about the material. “From the data sheet of the regranu- late, you can read out a few things, for example about mechanical and thermal properties. How- ever, you cannot find a real indicator for the weldability quality in the data sheet. Only the test will show. That is also the reason why there are ultrasonic laboratories. Customers come to us for welding tests to check process properties and whether their requirements have been met. There is, of course, a lot of in-house experience due to many years of ultrasonics, so we can assess many things well beforehand. But when it comes to the weldability of recycled materials, we have broken new ground in our plastics laboratory.” Ultrasonic welding tests have also been done on bio-based plastics, with blended and 100% bio-based materials. Ochs said: “The tests showed that the blends were quite close to the standard plastics. The pure bioplastic only performed half as well in terms of tensile force. Nevertheless, the
Left: Hermann Ultraschall had to deal with a demanding specification in the Bosch FreshUp clothes freshening device
Above: Jochen Ochs, Head of Application Technology Plastics at Herrmann Ultraschall- technik
May 2023 | INJECTION WORLD 39
IMAGE: BOSCH
IMAGE: VDMA
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