Yet, anybody intending to employ graphite electrodes successfully and economically must take into account the entire process chain - beginning with the design and planning via the right machines and refined tools equipped with high performance coatings and extending to measuring technology for quality control and the training of personnel. On this the experts from Zecha Hartmetall-Werkzeugfabrikation GmbH, CemeCon AG, GF Machining Solutions GmbH and CIMTRODE GmbH universally agree.
"Less melting loss, thermal stability, higher cutting rates virtually without wear - it is hardly any wonder that today graphite is preferred over copper for electrode manufacture. The material offers a host of advantages that have a direct and positive impact on efficiency," says Arndt Fielen, Sales Manager at Zecha Hartmetall-Werkzeugfabrikation GmbH, the high-precision, mini-dimension tool specialist. Probably one of the key advantages is that graphite provides a ready-for-erosion electrode straight from the milling machine. This means that erosion is possible without any manual reworking at all," explains Daniel Gruber, owner of CIMTRODE GmbH, graphite processing experts, for example, of high quality measuring technology for tool and mould-making. It offers many users enormous saving potential and, in addition, usually also increases the dimensional accuracy, and in turn the quality of the products being manufactured.
Another key advantage of graphite is the possibilities of electrode design. Tool and mould-makers used to have to manufacture hundreds of individual copper electrodes, but today, thanks to graphite, the electrode number can be radically reduced. This is because the established HSC milling technology makes graphite machining infinitely variable and enables the manufacture of electrode geometries that would not be possible with copper. "There are examples where the electrode geometries of over 100 copper electrodes have been combined into just four geometries in graphite," says Benjamin Sendler, Head of Application Technology at GF Machining Solutions GmbH, manufacturer of high quality machines for the milling and spark erosion.
Coordination for best results
Exploiting the advantages to their full calls for the right planning and the coordination of a whole range of parameters is essential. Arndt Fielen: "The machining of graphite, for example, enables significantly higher removal rates and more intricate shapes. However, the quality of the tools must also be up to the job. Sophisticated geometries, such as, for example in the SEAGULL series, are only one of the important factors ensuring high precision." The extraordinarily short cutting geometries married to the ultra-low mill cutter tolerances of SEAGULL mill cutters enable the problem-free manufacture of the finest ribs and highly complicated electrode geometries.
Diamond coatings are a decisive factor, here. This is because the high abrasive nature of graphite would hardly make machining possible unless there was effective wear protection. In order to ensure the high precision of the tools even after the coating, it must not influence the micro-geometry in any way. "Our multilayer diamond coatings are deposited on the tools' end dimensions and retain the micro-geometry - and can be reproduced at any time. This produces an unbeatable combination of perfectly ground tool, high quality and extremely smooth coating that ensures the excellent surface quality of the milled electrode," says Thomas Schaaff, Area Sales Manager at CemeCon AG, experts for innovative coating solutions for machining tools.
Nevertheless, even the best tool fails to produce top results if the machining parameters as well as the quality of the processing machines are not just right. For example, if the settings and the programming are not coordinated the system will at best fail to work efficiently because the tool wear would be excessive or the removal rate would be too low, but also tool breakage and destruction of the electrode would also be conceivable. Benjamin Sendler: "We provide solutions both for milling and spark erosion, and as a tool and mould maker partner know how important it is to coordinate all the factors. To do this all those involved, i.e. machine manufacturers, mill cutter manufacturers, control manufacturers measuring instrument manufacturers, and last but not least, the user himself must collaborate closely - this means from planning through to execution as only this will produce truly impressive results."
For intricate electrodes with µm-tolerances in particular, all the influencing factors must come together perfectly. Only a superb quality control can detect errors at an early stage and, if necessary, initiate an adjustment of the parameters. CIMTRODE has specially designed a measuring and testing system for mould and tool-making called C-View. It enables such things as the control and evaluation of wear on mill cutters or drill bits. In addition, it permits an exact evaluation of the electrode surfaces before erosion takes place. "This offers enormous advantages for the user and enables considerable improvements in quality and process capability," states Daniel Gruber.
In order to be able to implement the high quality and precision required by tool and mould-makers as efficiently as possible, more and more firms are turning to standardisation and automation. This leads to advantages for individual manufacture that so far have usually only been reserved for series production. Thomas Schaaff: "Process capability is enormously important, especially as automation increases. Our diamond coatings make a decisive contribution here. The uniform quality and the superb properties offered by the multi-layers mean that the tools achieve high service cycles and thus can be employed longer and are more reliable." This contributes to a high process capability and stability in order to enable the fully automatic manufacture over the weekend, for example.
Apart from this, new processing variants aim to better unify productivity and precision. "An innovation of recent years has been the wet milling of graphite and opens up many new possibilities. It enables more flexibility in processing steel, copper and graphite on one machine and in the process reduces the tool costs significantly. It could be the solution for all those who have hitherto been unable to benefit form the material advantages of graphite - perhaps because investing in the requisite erosion machine and an additional new milling machine for dry processing would have been too cost-prohibitive," says Arndt Fielen explaining the new paths that graphite processing open up.
Nor has sink erosion development stood still, either: "Modern generator technology can already save time by up to 40 per cent without loss of quality and cater for smaller electrode undersizes. New erosion strategies are also very promising and can produce special surface textures that significantly reduce the wear of injection and pressure die-casting tools as well as demoulding forces," adds Benjamin Sendler.
For more information:
ZECHA Hartmetall- Werkzeugfabrikation GmbH
Tel: +49 (0)7232 3022-0
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