Reducing greenhouse gas emissions has become an objective throughout the world. In many places, there are now discussions about imposing taxes on emissions, with implications for the development of new cutting tool technologies.
The German government has set itself the objective of reducing carbon dioxide emissions in Germany by 55% by 2030. This has a considerable impact on the development of machining tools, as new fields of application are emerging and existing ones need to be adapted. Alternative drives, new, lighter materials and concepts that save energy and resources are now more in demand than ever before. Developers see great potential in design modifications to tools, new coatings, new machining strategies and digital solutions which respond to the existing framework conditions in real time.
Ramping milling cutters increase tool life by up to 200%
The current trend is for new, lightweight aluminium-lithium alloys. These materials quickly overwhelm conventional tools. This results in an increasing demand for high-performance tools specifically designed for this range of applications.
For instance, aircraft components made of aluminium alloys often have machining volumes of up to 90%. Depending on the required component geometry, numerous bevels and cavities need to be milled out of the metal, with the goal of ensuring stability and reducing weight. To manufacture the components economically and to a high quality, they need to be machined using high-speed cutting (HSC) processes involving cutting speeds of up to 3,000 metres/min. Cutting values that are too low lead to build-up on the cutting edge and therefore result in rapid wear and frequent tool changes. This results in high costs due to long machine running times. Machine operators specialising in aluminium therefore have good reason to demand above-average cutting data and tool life from their tools, as well as particularly high process reliability.
With the design of the M2131 ramping milling cutter, the tool developers at Walter have shown how such complex requirements can be dealt with. The 90-degree milling cutter is equipped with a new class of indexable inserts, with the grade designation WNN15. This refers to a new PVD coating, which is manufactured using the HIPIMS method. The term HIPIMS stands for “High Power Impulse Magnetron Sputtering”, a technology based on magnetron cathode sputtering.
The special feature of the physical coating process is that it produces an extremely dense and smooth PVD coating, which greatly reduces friction and the tendency to cause built-up edges. At the same time, this method increases cutting edge stability and resistance to flank face wear, enabling a maximum metal removal rate as a result. Field tests have confirmed the advantages of HIPIMS indexable inserts compared to standard types: increases in tool life of up to 200% were achieved.
“We are seeing an increasing demand for high-performance tools for machining aluminium, particularly in the aerospace industry but also increasingly in the automotive industry,” explains Wolfgang Vötsch, Senior Product Manager for Milling at Walter.
Dynamic milling – milling strategy with a focus on efficiency
Many sectors, particularly the supply industry, are under pressure to provide increased process reliability and faster machining – at ever lower costs and with consistent quality. The demands for surface quality and dimensional stability are often increasing at the same rate as requirements for process reliability and cost efficiency. Moreover, there is a growing need for lightweight or heat-resistant materials. However, these materials from the ISO M and ISO S material groups are often difficult to machine precisely because of these properties.
Dynamic milling provides a solution in this area, offering both productivity and process reliability. This is why a growing number of metalworking companies are relying on this method.
High-performance cutting vs High dynamic cutting
The main differences between conventional high-performance cutting (HPC) and high dynamic cutting (HDC) are in the movement of the milling cutter and the forces generated. During HPC, the milling tool moves with relatively low depths of cut. During HDC, the CAD/CAM control system adapts the machining paths so that the tool moves according to the shape of the workpiece. This prevents non-cutting time, or at least reduces it. Moreover, the depth of cut is significantly greater during HDC than during conventional HPC, meaning that travel distances are also reduced because the complete tool length can be used.
The engagement angle is usually very large during HPC. The forces that occur in the process are accordingly high. This in turn quickly causes signs of wear to appear on the tool and the machine spindle. Dynamic milling, on the other hand, is characterised by a high level of process stability and a long tool life. The engagement angle chosen for HDC is normally small, meaning that the forces which impact the tool and machine are much lower than for HPC. Higher cutting parameters, less non-cutting time and increased process stability result in a much higher metal removal rate for HDC milling compared to HPC.
Adaptive feed control: Cutting data optimisation using live data
Automation, digitalisation and networked processes have been everyday aspects in many areas of metalworking for a long time. In particular, the hardware and software used to collect and analyse live data have produced huge leaps in performance.
The Comara iCut software tool demonstrates how this provides opportunities to optimise processes. The adaptive feed control analyses incoming machine data in real time and adjusts the machining accordingly. This answers one of many users’ key questions. Namely: how can you get the most out of a machine without making major changes to the process or carrying out complex reprogramming work?
The iCut software enables the machining time per workpiece to be significantly reduced. This software is integrated into the existing control programme and applies the data from this for the machining process. During the first cut, iCut “learns” the idling output of the spindle and the maximum cutting efficiency per cut. Subsequently, it measures the spindle output up to 500 times per second and automatically adjusts the feed in each case. This means that the machine always operates at the maximum possible feed for each tool. Should the cutting conditions change (depths of cut, machining allowances, wear, etc), iCut adjusts the speed and output in real time. This not only has a positive effect on the machining time for the workpiece; the optimised milling characteristics also increase the process reliability. The forces acting on the spindle are more constant and this also results in a longer service life.
If the tool is in danger of breaking, iCut reduces the feed straight away or stops the action altogether. Florian Böpple, Digital Solutions Manager at Walter, says: “We have already achieved astonishing increases in efficiency for customers using iCut. If the machining operation is compatible, a 10% reduction in machining time is always achievable. We have already managed to reduce machining times by double this amount. When the quantity is high, this frees up considerable machine capacity.”
Moreover, this works irrespective of whether Walter tools are used; all that is necessary is for the machine’s system requirements to be met.
Milling with “Xtended Technology”
Walter recently showed the potential of the tools themselves with the entirely new generation of Xtra-tec XT milling cutters. These cutters combine design improvements with high-performance cutting tool materials. This means that the focus is always on increased productivity and process reliability. The most striking design feature is the installation position of the indexable inserts, at a greater incline and with a larger contact surface. This reduces the surface pressure in the seat while increasing the stability. The larger screw hole cross-section stabilises the indexable insert and the longer screws hold it in place more securely. The cutter body has also been made stronger, now with much more material behind the insert seat.
Besides increased process reliability, the special installation position of the inserts also allows for the addition of an extra tooth, thereby increasing productivity. The precise 90-degree shape of the shoulder milling cutter helps to reduce what would otherwise be additional required finishing operations. Clamping screws which are easier to access optimise handling and help prevent assembly errors.
Another new feature, which applies to the face milling cutter M5009 in particular, is the smaller indexable inserts which can be fitted to the milling cutters. These continue the current trend towards reduced machining allowances. The M5009 milling cutters combine small depths of cut with the economic advantages of double-sided indexable inserts – with eight usable cutting edges rather than the usual four. Thanks to these cutting edges, as well as a reduced number of finishing operations, the millingw cutter achieves increased efficiency.
Walter’s commitment to innovation also extends to sustainability. As part of Walter Green, the production and supply chain of the Xtra-tec XT milling cutters is CO2-compensated.
These examples illustrate where we are heading in the metalworking industry – with respect to tools, machining strategies and the field of digital innovation. At the same time, they highlight approaches where the opportunities lie and how the trends and challenges of the future can be dealt with successfully.