Moldino “Process optimisation makes us future-proof”
At Zimmermann Formen- und Werkzeugbau in Gladenbach in central Hesse, the milling processes have been put under the microscope.
The entry into adaptive milling was assisted by the process optimisation approach of Moldino Tool Engineering Europe. Milling is now up to 70 % faster.
For the production of the yellow German telephone boxes, Zimmermann once set a record in the manufacture of the world’s largest injection mould.
As milling represents a huge cost factor, this must also be considered in economic terms. In addition to the CAM area, the focus here is on tools. After all, the process can just as easily be influenced by tools. Not least for this reason Moldino Tool Engineering Europe sparked the interest of Zimmermann, because the tool manufacturer offers to optimise the milling processes on site based on concrete projects.
“In our first joint optimisation project with Moldino Tool Engineering Europe, I wanted to finally tackle a topic in which both the CAM system and the tool play an important role: trochoidal milling,” reports Sören Leinweber, who is responsible for the CAM department at Zimmermann. “We hadn't done this before because WorkNC had limited capabilities and we didn't have the tools. However, trochoidal milling has been greatly improved with the new Waveform roughing and finishing strategy that WorkNC now has.” And so this strategy was used as well.
The workpiece was a small slide (approx. 230 mm x 115 mm x 115 mm) made of the plastic mould steel 1.2312 (40CrMnMoS8-6), which had previously been roughed and finished in a quenched and tempered condition (tensile strength 950 to 1100 N/mm2) on a 5-axis DMC 75 V linear with Z-constant soft roughing and finishing. From a construction point of view it was a new part whose accuracies were different. For the fit, the accuracy was plus 5/100 mm.
At Moldino Tool Engineering Europe, an elaboration was made for trochoidal milling. In addition to the complex geometry, the specifications included the shortest possible processing time. Therefore the EPSM, a solid carbide milling cutter was selected for roughing, which due to its geometry can be used to great effect for adaptive milling. And thus the EPSM was able to impress during the test on the new tool — which took place directly on the real workpiece. Due to the positive cutting angle and the sharp cutting edge of the EPSM, a stable process was achieved with a very soft cut and relatively low forces on the workpiece. The latter was extremely important because the complex geometry of the slide was very difficult to clamp. In addition, there were fewer vibrations compared to normal insert milling. Otherwise the workpiece might have been levered out of the clamping. In order to achieve a vibration-free process, the tool diameters were selected on the basis of the required insert depths and machine conditions. The combination of improved chip evacuation and process-optimised parameters ensures an optimal heat transfer into the chip. As a result of the low heat transfer into the part and the cutting tool, a longer tool life is achieved, the company promises.
For pre-finishing, the 4-edged ball tools of the EHHB series were then used, which were run at very high feed rates, i.e. high fz and high lateral ae with the strategy Z-constant. Without having to remove the trochoidally produced steps with an additional tool, it was possible to move the pre-finishing chip directly after roughing with the EHHB balls in order to have a constant measurement in the finishing area afterwards. This has a positive effect on tool life and surface quality of the finishing process. Everybody was enthusiastic about the fact that this is possible with ball tools.
The fine finishing — also with Z-constant — was then carried out by the ball cutters of the HGOB series. Due to the use of in-house coatings — in this case a PN coating with a low coefficient of friction — a high surface quality was achieved. Originally the roughing had been done with a diameter of 35 mm and there had been at least one R17 in the corners everywhere. Now a corner radius of 8 mm is roughed, which of course is a huge advantage for finishing. For example, Zimmermann has clearly become much faster at roughing and has also gained a great deal in post-processing: Compared to before, time savings of 40 % were achieved over the complete process.
Furthermore, the mould and die maker was impressed by the active use of Moldino Tool Engineering Europe: “They really came here with know-how, team and tools, looked at the current situation, told us what was possible and what could be done, and then implemented the solutions in the process,” enthuses Sören Leinweber. “Without this on-site support, we would not be where we are today when it comes to trochoidal milling. In addition, the enormous time advantage achieved also has an extremely positive effect on production costs.”