Now more than ever, new developments in manufacturing are dictated by environmental issues. Consumption, emissions, weight, recycling – all key terms that begin the list of specifications for any new product. This has led to increasing use of new materials such as CGI (compacted graphite iron), ADI (austempered ductile iron) and heat-resistant cast steel in the automotive industry, composite materials and titanium alloys in the aviation industry, and super-alloyed steels and titanium alloys in the power plant industry.
Thanks to these new materials’ enhanced mechanical and thermal properties, manufacturers can use the materials to design thinner walls, reduce weight and boost application pressures and temperatures. The improvements made to these properties compromise the materials’ machineability – in some cases, the trade-off is stark. Compared to those of older materials, the downtimes and cutting conditions manufacturers see today are much lower; the resulting spikes in costs, however, are simply too high.
Here, the cutting material plays a particularly important role. The most important shift in development: optimizing the cutting materials’ resistance to wear at high temperatures and their tribological properties. Basic steps taken to boost the materials’ resistance to wear – such as using a more rigid substrate or a thicker coating – have proven unsuccessful. The reason: these steps cause the materials to become less resilient, thus introducing unacceptable levels of risk into processes. Truly driving productivity to required levels involves improving two ratios: rigidity to high temperature properties; rigidity and toughness.
This is where the enormous potential of two of the latest advances in coating come to the fore: shotblasting of CVD coatings and PVD-Al2O3. The former was launched under the brand name Tiger•tec® by Tübingenbased WALTER AG in 2001. Tiger•tec® uses an ancillary mechanical treatment to significantly improve internal stress and tribological properties. As a result, processes are much more reliable as comb-type fractures, mechanical failures and built-up edges are kept to a minimum. Four years later, WALTER AG launched PVD-Al2O3, a coating procedure that opens up new opportunities for applications thanks to its considerably faster cutting speeds. Compared to the conventional TiCN and TiAIN coating systems, PVDAl2O3 boosts application temperatures to by around 150-200 °C while maintaining the excellent resilience PVD is known for.
In a similar way to the cutting materials, improvements have been made with the microgeometry of the blades. Another area with great potential is optimizing cutting surface microgeometry in terms of tribology. Lots of these materials have high alloy content so they tend to “get stuck” – in other words, form built-up edges. This can have a dramatic impact on life expectancy and surface finish. Cooling lubricants improve the situation, but their use is hotly debated. Steinbeis, the TU Dresden, Shell and WALTER AG joined forces to investigate how structuring the cutting surface and developing solid lubricants can improve an indexable insert’s tribological properties. By structuring the cutting surface’s top layer in a particular way, the team was able to make the solid lubricant more effective and double tool life travel.
Prof. Dr.-Ing. Ulrich Günther
Steinbeis University Berlin
Steinbeis Transfer Institute Production and Engineering (Berlin)
stz778@stw.de
Jörg Drobniewski
M. Löffler
Walter AG (Tübingen)
Charsten Wienbreyer
Shell Lubricants (Hamburg)
Dipl.-Ing. Gunnar Meier
Technische Universität Dresden (Dresden)