Due to an excellent ratio of high strength and low density, Ti-6Al-4V is suitable for many industrial applications, especially in the aerospace industry. However, Ti-6Al-4V is also characterized by a very low thermal conductivity and high chemical reactivity which is why the titanium alloy is considered to be a hard-to-cut material. Machining Ti-6Al-4V leads to high cutting temperatures, which leads to a rapidly progressing thermo-chemical induced tool wear. To reduce the thermal load and to enhance the cutting performance, suitable cooling strategies are a necessity. A novel, highly efficient cooling approach is to apply sub-zero metalworking fluids (MWF) at liquid state but at supply temperatures well below 0 °C. These sub-zero MWF inhibit high cooling effects due to their low supply temperature in superposition with a beneficial wetting behavior. In this work, the application of a sub-zero cooling strategy is investigated when milling Ti-6Al-4V. The influence of both down milling and up milling is investigated under a systematic variation of the cutting speed and feed per tooth. For comparison, the experiments are also conducted using a cryogenic CO2 cooling. The performance of both cooling strategies in dependence of the milling process is described on the basis of the occurring forces, the resulting tool wear, and the surface quality achieved. The results show that the sub-zero cooling can successfully improve the machinability of Ti-6Al-4V even at elevated cutting parameters and unfavorable cutting conditions. As a result, sub-zero milling clearly outperforms the cryogenic CO2 cooling, since less tool wear and an overall lower surface roughness are observed. Consequently, when using a sub-zero cooling strategy, higher metal removal rates, longer tool life, and better surface qualities are achievable.
Due to an excellent ratio of high strength and low density, Ti-6Al-4V is suitable for many industrial applications, especially in the aerospace industry. However, Ti-6Al-4V is also characterized as a hard to-cut material. This is mainly attributed to its very low thermal conductivity and high chemical reactivity, especially at elevated temperatures. Machining Ti-6Al-4V leads to high cutting temperatures and thermal loads of the tools within the cutting zone. This enhances a rapidly progressing, thermo-chemical induced tool wear reducing tool life and productivity. To enhance the cutting performance, suitable cooling strategies are a necessity to reduce the thermal load and hence to improve the machinability of Ti-6Al-4V. A novel, highly efficient cooling approach is to apply sub-zero metalworking fluids (MWF) at liquid state but at supply temperatures well below 0°C. These sub-zero MWF inhibit high cooling effects due to their low supply temperature in superposition with a beneficial wetting behavior. Within this paper, the application of a sub-zero cooling strategy is investigated and compared to a cryogenic CO2 cooling. The performance of both cooling strategies is analyzed when milling Ti-6Al-4V by systematically varying the cutting parameters and the milling strategy. The milling process is described on the basis of the occurring forces, the resulting wear and the surface quality. The results show that the sub-zero cooling outperforms the cryogenic CO2 cooling, especially at elevated cutting parameters and unfavorable cutting conditions. Less tool wear and an overall better surface quality are observed for sub-zero milling when being compared to cryogenic milling.
In this paper the design of a Time-Domain Full-Field OCT (TD-FF-OCT) setup for non-contact volumetric layer thickness measurement is presented and quantified in terms of achievable accuracy and performance. The capabilities of the instrument regarding its measuring accuracy are verified using foil thickness standards of different strength. Afterwards, a technical application of measuring a thin and rough varnish coated PET foil (foil thickness t f oil ≈ 150 µm, rough varnish layer thickness t varnish ≈ 10 µm) is carried out. Since the device is designed to conduct areal measurements, the thickness can be accurately determined over several measurement points. The results are compared with results achieved by applying an alternative but destructive and more time-consuming measuring method (evaluation of microscopic images of respective foil slices produced by using a microtome). Finally, the achievements are summarized and identified optimization potential is highlighted.
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