“With our total of 117 employees, we provide both the entire fischer Group and external customers with newly-made articles and repairs”, explains Bernd Ströhlein, head of the tool manufacturing department. “Here at the Horb location we mainly build high-cavity precision injection moulding tools for fastening technology and the automotive area, as well as silicon cartridge tools for chemical fastening technology.” Punch press tools produced for heavy load fastening technology are also manufactured. Milling is regarded as one of the most important production processes at fischer. Consistent use is made of automation when doing this, as it is during the eroding process. In Horb they endeavour to manufacture all parts which have a long service life in the automated, 16 metre long production cell. However, this assumes that the milling process runs with complete process reliability. Since the collaboration with MMC Hitachi Tool, fischer has made another huge step forward in this area. Within this framework, the milling processes have been redeveloped on the basis of 2 specific components.
The experience that has been made with the Japanese tool manufacturer has been positive throughout. During the hard machining of grooves in deep-lying cavities, for example. Here, time and time again fischer had the problem that during the milling of this groove, which contains the stranded wire for inductive heating of the mould, breaks were occasionally occurring in the induction tools. When this groove is being milled, it is important that the stranded wire which generates the magnetic field does not have too much air but also does not have too little. Induction moulding tools such as this are one of the specialities of fischer Werkzeugbau, and achieve extremely high-quality finishes when the combination of injection moulding and reaction technology is used. In this case, it is a 1k tool with four cavities for manufacturing ventilation elements in car interiors.
The process optimiser from MMC Hitachi Tool used the ‘Production 50’ optimisation concept which has been specially developed for the milling area. They carried out a situation analysis in which the component geometries were also analysed. First, there was the difficulty of machining 1.2343 ADG (X38CrMoV5-1) which had been pre-hardened to 52 to 56 HRC in the deep cavity, which requires long tools. It had to be roughened and also finished to the final dimension. Previous experience had shown that from a tooth length of 40 mm, tool breakages were occurring with the 4 mm torus milling cutters that have been used to date and also the ball cutters with the same diameter. Various attempts with selected types of milling device were carried out. The groove geometry was also checked when doing this, and minor alterations were made together with employees from the tool construction area, without any adverse effects on functionality. For example, the angle of the groove has been changed a little in order to stabilise the milling process. In the 3-axis strategy that was used, as much attention as possible was paid to having smooth tool paths, radii and smooth entry and exit movements. Furthermore, the NC program was dynamically designed so that the machine always achieves the required feed values.
And then there were the ETRP-4030-50-0908-TH from MMC Hitachi Tool, the 3 mm torus milling cutters with a TH coating from the EPOCH 21 series, which proved to be a real highlight. This was because they left all of the other test candidates standing with regard to machining speed and service life. It was possible to roughen and finish the stranded wire groove with absolute process reliability with the 3 mm ETRP milling cutters, even with a free length of 50 mm, i.e. the longest tool. In some cases this was even possible with a feed value of 1,200 mm/min without a single tool break. The speed has also been improved considerably – 14.5 hours was previously required in Horb to machine the cavity for the stranded wire, which can now be milled in ten hours. Even the profitability calculation that was carried out with regard to the Production50 concept was totally impressive: Since the tools now last for significantly longer, the tool costs for manufacturing the wire strand cavity alone have been reduced by about two thirds. The machine hours that are saved have also led to a 30 percent reduction in machining time. There have even been economic benefits in nozzle manufacturing – 24 nozzle seats can be milled using a single milling cutter with MMC Hitachi Tool. The tool was still usable afterwards, but not for fine finishing with narrow tolerances. Previously a tool would sometimes have lasted for 6 trims – or perhaps only 1. Neither the milling process nor the wear behaviour were reproducible. “Thanks to the newly developed and well documented processes which have been created together with MMC Hitachi Tool, we can now mill the wire strand cavities and also the nozzle seats automatically with process reliability and therefore unmanned”, says a delighted Bernd Ströhlein. “And even on different machines, which is particularly important to us.”
Mr Hauke Steinigeweg
MMC Hitachi Tool Engineering Europe GmbH
Tel. +49 (0) 21 03 - 24 82-0