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Technical article by acp systems AG: a new, fully integrable module for cryogenic cooling
Fully integrable CO2 cooling module for internal and external coolingMore efficient, productive and sustainable CNC machiningCryogenic cooling with CO2 offers decisive economic and environmental advantages, particularly when machining difficult-to-machine metallic materials and plastics. These advantages can be effectively harnessed in industrial practice through an innovative CO2 cooling module that is fully integrated into CNC machining centres and lathes in terms of machinery, control systems and safety technology. The new cooling unit, which was developed as part of a research project, operates for both external and internal cooling with automatic tool change in a manner comparable to systems for conventional cooling lubricants and can be combined with these where required.
Cryogenic cooling using CO2 is utilised, amongst other things, in a new tool turret. Targeted cryogenic cooling directly at the cutting edge reduces thermal stresses, thereby significantly improving process stability, cutting performance and tool life, particularly when machining high-strength materials.
High-strength materials, rising demands on component quality, the desire for maximum material removal rates, stricter requirements regarding energy and resource efficiency, the reduction of the CO2 footprint and, last but not least, increasing cost pressures are presenting new challenges for machining technology. Cryogenic cooling with CO2 is regarded as the key to efficiently addressing these challenges. “Cryogenic cooling makes it possible to push the technological boundaries in machining and thus achieve significant improvements in productivity, cost-effectiveness, sustainability and health and safety,” explains Lucas Günther, a project engineer in the Machining Technology Research Group led by Prof. Dr.-Ing. Uwe Teicher at the West Saxon University of Applied Sciences Zwickau (WHZ) and at the university’s Research and Transfer Centre (FTZ). His colleague Andreas Zinke adds: “Due to the considerable interest in a fully integrated cooling system solution, both within the machine tool industry and amongst end-users, the WHZ and the FTZ have initiated a research project in collaboration with the cooling system manufacturer acp systems, the machine tool manufacturer Chiron, the manufacturer of clamping technology and rotary unions Ott-Jakob, and other industrial partners from the fields of tool manufacturing and safety technology. The ‘Industrial Working Group on Machining with CO2’, founded in Zwickau in 2015, was also involved.”
Fully integrated, CNC-controlled cryogenic cooling
The aim was to develop a cryogenic cooling solution for external and internal cooling that could be fully integrated into machining centres and lathes – in terms of media supply, control and safety technology – and controlled via CNC, just as is the case with systems for conventional cooling lubricants. To achieve this, various challenges had to be overcome. The first related to the size and space requirements of the cooling module. Whilst it was developed for use in a Chiron Mill 800 with the HSK 63 tool interface, it must be adaptable without significant effort to machine designs from other manufacturers and to other interface systems. “In addition, we have developed a suitable media distributor for integration into the machine. This allows the cryogenic cooling to be selected – just as with conventional cooling solutions – either as external cooling on the tool or as internal cooling through the tool,” says Lucas Günther, describing a further challenge. This includes the option of operating a machining centre in a combined manner – using both cryogenic and emulsion cooling or minimum quantity lubrication. The integration of the system into the control and safety systems was achieved via standardised interfaces and CO2 safety sensors. “This means the cryogenic cooling system can be controlled entirely via the machining centre,” explains Andreas Zinke. “Furthermore, the safety systems of the machining centre and the cooling system are linked. If one of the systems shuts down, the other is also automatically shut down.”
The cooling module developed can be adapted with minimal effort to machine designs from various manufacturers and interface systems (e.g. the Chiron BAZ Mill 800 with the HSK 63A tool interface). The workplace exposure limit for CO2 of 5,000 ppm is reliably maintained by the integrated safety technology.
The cooling module, which is fully integrated in terms of machinery, control systems and safety technology, operates in a manner comparable to systems for conventional cooling lubricants when used for internal cooling with automatic tool change, and can be combined with such systems where required.
The limit value of 5,000 ppm CO2 is reliably adhered to
To complement the cooling module, a concept for the safe operation of machine tools with cryogenic CO2 cooling was developed at the FTZ on the basis of extensive investigations and tests. To determine the potential risk to production staff, the researchers worked with two test scenarios: in the first, CO2 was used in small, medium and large quantities in machine tools with open or semi-open working spaces. In the second test setup, the working space was enclosed; here too, different quantities of CO2 were used. In each case, the CO2 concentrations were measured in the machine and hall environments whilst the external extraction system was switched on and off. “Building on this, we defined which safety technology is required, how it should be deployed to ensure safe operation, and where it must be positioned. Accordingly, acp systems has integrated CO2 monitoring sensors for concentration measurement and shut-off technology into the overall system,” reports Andreas Zinke. “The occupational exposure limit for CO2 of 5,000 ppm in the ambient air is reliably adhered to. In general, the quantities of CO2 used in machining are to be regarded as low.”
Boost productivity, cost-effectiveness and sustainability dramatically
Research into cryogenic cooling has been underway at the WHZ and the FTZ for 15 years. Extensive fundamental studies using different materials and across various machining applications have demonstrated the effectiveness of CO2 cryogenic cooling. In particular, when machining difficult-to-machine metallic materials – including stainless steels, nickel, cobalt and titanium alloys – as well as plastics, fibre-reinforced composites and polyetheretherketone (PEEK), higher chip volumes, reduced tool wear and longer tool life were achieved compared with conventional cooling lubricants (KSS). These advantages were confirmed by various application- and component-specific projects carried out with industrial partners. Furthermore, the cooling process leaves no residue, which minimises the cleaning effort required for components and machine tools and significantly facilitates the recycling of swarf. “In addition, the use of CO2 often results in improved surface quality and reduced burr formation,” adds Lucas Günther.
The cooling technology also offers advantages from an environmental and occupational health and safety perspective. The recycled, liquid CO2 used for cryogenic cooling is produced in chemical manufacturing processes and during energy generation from biomass. In contrast, conventional cooling lubricant is a chemical product that must be disposed of at the end of its service life. Furthermore, components of cooling lubricants – such as additives or bactericides – can pose a risk to staff. Cryogenic cooling also performs better in terms of its CO2 footprint. “Initial investigations and comparative calculations on energy consumption have shown that, when using medium-sized oil/emulsion cooling systems, power consumption is in the range of several kilowatts; for high-pressure cooling systems, this can even reach 10 kW. Cryogenic cooling, by contrast, consumes less than 100 watts,” reports
Andreas Zinke. This allows for significant energy savings, which has a positive impact on the CO2 footprint.
With the newly developed CO2 cooling module from acp systems, the machining industry now has a solution that can be fully integrated into any machine tool, lathe or machining centre – regardless of the manufacturer – and operated reliably via CNC control. It thus enables significantly higher performance compared with conventional cooling using coolant, whilst also delivering the technological, economic and environmental benefits of cryogenic cooling.
Cryogenic cooling enables higher productivity, shorter machining times and longer tool life, as well as improvements in process reliability, sustainability and health and safety.
Cryogenic cooling also offers advantages when it comes to energy consumption and the carbon footprint.
About acp systems
With its solutions, acp systems AG ranks amongst the global technology leaders in advanced clean production, including process automation and system integration. Founded in 1997 and headquartered in Germany, the company’s core technologies include the resource-efficient quattroClean snow jet cleaning system, cryogenic CO2 cooling, high-precision micro-dosing and intelligent handling solutions, for example for flexible materials and films. acp supports companies – including those in the semiconductor, electronics and automotive industries, as well as in precision optics and medical and pharmaceutical technology – in the development, planning, design and integration of highly automated, sustainable manufacturing processes.
Source | Sauter Feinmechanik GmbH, acp_FB_kryogene Kuehlung, Schulz