This paper discusses an investigation into the capability of liquid nitrogen (LN2) and liquid carbon dioxide (LCO2) as a coolant in machining. A comparative analysis of the heat-transfer rate was made utilizing cooling of a controlled heat source with an integrated temperature sensor. The analysis was coupled with experimental in-process temperature measurements in cryogenic milling of titanium alloy Ti-6Al-4V (ß). The results indicate that cooling capability differs between these two cryogenic media, in both the observed cooling rate as well as in the achieved steady-state temperature.
COBISS.SI-ID: 16614427
A novel single-channel supply of pre-mixed (a) liquid carbon dioxide (LCO2) and (b) oil - delivered via minimum quantity lubrication (MQL) - represents a significant advancement in cryogenic-machining technology. In this proof-of-concept study, an attempt is made to advance the understanding of the oil solubility in LCO2 and to analyze the oil-droplets and their impact on machining performance. The results indicate that the physical and chemical properties of oil distinctively affect its solubility in LCO2. The achieved solubility further influences the achievable oil-droplet size and distribution and tool life.
COBISS.SI-ID: 16781851
Efficient cooling and lubrication techniques are required to obtain sustainable machining of difficult-to-cut materials, which are the pillars of aerospace, automotive, medical and nuclear industries. Cryogenic machining with the assistance of lubricated Liquid Carbon Dioxide (LCO2) is a novel approach for sustainable manufacturing without the use of harmful water-based metalworking fluids (MWFs). In case of unavoidable use of MWFs under high pressure, such as turning finishing processes of difficult-to-cut materials, the pulsating high pressure delivery of MWFs prolongs the tool life and enables the control over chip length to prevent surface damage of high value-added parts. In this paper, sustainability assessment of both advanced principles was carried out, considering overall costs and operational safety. Experimental tests were executed on difficult-to-cut materials in comparison to conventional flood lubrication. For both techniques, longer tool life compared to flood lubrication was observed additional cleaner production and higher part quality led to reduced long-term overall costs. These advanced machining technologies are also operation safe, proving to be a sustainable alternative to conventional machining.
COBISS.SI-ID: 16944155
An investigation is made into the lubrication capabilities of solid-lubricated liquid carbon dioxide (LCO2) incomparison toflood lubrication, straight LCO2and oil-lubricated LCO2(MQL). The coefficient of friction isdetermined via tribological experiments, similar to machining, using an open tribometer which features anuncoated carbide insert sliding against a workpiece. Tribological experiments reveal superior performance ofsolid-lubricated LCO2. The milling experiments as well indicate that solid-lubricated LCO2significantlyreduces wear. The machined-surface topography is examined using high-magnification SEM, which showsno presence of adhered solid particles on the workpiece surface, providing a completely dry machining pro-cess.
COBISS.SI-ID: 15739395
This study compares drilling performances of carbon fibre reinforced plastic (CFRP) composites under dry and cryogenic environments. Industry-relevant outcomes namely thrust force, hole quality (cylindricity-CYL, circularity-CIR, and average surface roughness-R [sub] a) and inverse delamination factor, are analysed to adopt a green machining technique. Measurement of industry-relevant hole quality parameters have not been explored and explained for cryogenic machining of CFRP composites. To measure CYL and CIR deviations, points are selected on the chosen plane(s) with a spherical probe of the coordinate measuring machine. A pitch of 1 [mikro] m is taken between two neighboring points for measurement. R [sub] a values are measured using surface roughness tester, and inverse delamination factors are measured using a vision measurement machine. R [sub] a values of holes are considerably decreased by 14-38%, and entry inverse delamination factor increased by 5-68% under cryogenic drilling when compared with dry drilling. These results advocate the suitability of cryogenic drilling for the industry.
COBISS.SI-ID: 17046555