of coolant, as well as component cleaning, are also reduced—to zero in cases where CO2
alone is used. In
these cases the swarf is 100% recyclable.
The Pressure Factor An important tech- nological advantage of the Cryo·tec cooling system lies in the way that the CO2
maintained for as long as possible on both the machine and tool side. After all, as soon as the pressure drops, ice begins to form and the CO2
with MQL, as well as a reduction in production costs of up to 30%, was also achieved when working with austenitic stainless steel.
pressure is
Surface fi nish in the area of the blade root after roughing, one dry and one with CO2
plus air cooling process.
supply gets clogged. At the same time, however, the CO2 throughput should not be greater than absolutely neces-
sary for the targeted cooling effect, since CO2 is expensive as
a coolant when compared with emulsion. “We invested a great deal of time and effort in the devel- opmental work when determining the correct nozzle diam- eter,” explained Schaarschmidt. “We are currently working on further optimizing pressure regulation and supply, as we would like to get even closer to the cutting zone. We are also focusing a lot of effort—in cooperation with lubricant manu- facturers—on developing new MQL oils.” Why new oils? “To date,” said Schaarschmidt, “they have been designed for high temperatures and therefore need to be adapted accordingly for CO2
cooling.” The Cryo·tec tools
are currently available only as special tools, as the corre- sponding machine/spindle technology is readily available only from Starrag. However, Walter is working to establish a tool connection standard.
Results
Experiments with turbine vanes made of martensitic stain- less steel—multi-axial turn-milling, raw component dimen- sions 18.7 × 3.15 × 3.15" (475 × 80 × 80 mm)—have shown that tool edge life can be increased by 30% over dry machin- ing while maintaining consistent cutting parameters, if the temperature at the cutting edge is reduced by 100°C using CO2
cooling. At the same time, production costs are reduced by 15%. A signifi cant increase in tool life in comparison
Overall, cryogenic machining has massive potential for heat-resis- tant superalloys (HRSA) and stainless steels. The task now is to verify this for further materials and applications in the ISO S and ISO M groups. The ability to transfer the application from the energy industry to the
automotive industry, as well as open questions regarding the technology, and handling of the CO2
of further developments.
Future Challenges By its nature, milling is an interrupted cut operation. The
inserts are continuously entering and exiting the cut. This will cause the inserts to heat up in the cut and cool as they exit. This effect is exacerbated by cryogenic CO2
cooling. Due
to the effect of large alternating temperatures, the carbide substrate and the coating expand at differing rates. This in turn leads to the formation of cracks in the coating layers and, ultimately, to cutting tool material failure. All cutting tool materials developed in the last few years have been designed for the high temperatures encountered in dry machining. Consequently, new cutting tool materials are now required that are specifi cally suitable for cryogenic CO2
cooling and
can withstand massive temperature changes. As Schaarschmidt noted, “Our major research and development topics for the future are standardization of tool concepts, and specialized cutting tool materials. This is because we expect the proportion of diffi cult-to-machine materials to increase to around 40% in turbines alone by the year 2020.”
Edited by Yearbook Editor James D. Sawyer from material supplied by Walter USA LLC.
will likely form the focus
77 — Energy Manufacturing 2015
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