Reducing effect of cooling and lubrication technology on energy consumption and carbon emissions during processing
March 11, 2023
Cooling and lubrication technology has always been one of the important technical means to improve the machinability of most difficult metal materials. However, under the multiple pressures of green, environmental protection, energy conservation and emission reduction, the modern machining field has put forward higher requirements for cooling and lubrication technology. How to systematically and comprehensively evaluate and analyze cutting cooling and lubrication technology to meet the challenges and needs of sustainable development is a new topic that must be considered by the current academic and industrial circles.
As one of the key technologies in the sustainable manufacturing technology system, cooling and lubrication has also attracted the attention of researchers at home and abroad. Relevant research has not only discussed the mechanism and effect of typical cooling and lubrication methods on the cutting process, but also carried out corresponding research and analysis on its environmental protection, energy consumption characteristics and carbon emissions
Reducing effect of cooling and lubrication technology on energy consumption and carbon emissions during processing
1. Energy consumption during processing
Cutting cannot be done without the machine tool, and the energy consumption of the machine tool varies significantly at different stages of the processing process (see Figure 7), such as the energy consumption at startup, the energy consumption in standby idle state, and the energy consumption when cutting materials. Among them, the energy consumption during cutting is the largest.
The change of cutting specific energy and machine power under different cooling and lubrication conditions and material removal rates. Among them, the cutting specific energy is defined as the energy required to cut the unit volume of material, and L, M, H and VH respectively represent the low, medium, high and super-high material removal rate. The increase of machine power is almost linear with the material removal rate, which is consistent with the research conclusions in the literature. From the perspective of cutting specific energy, CryoMQL consumes 1.97% more energy than Flood cooling and lubrication at a lower material removal rate. However, at a higher material removal rate, the energy consumption of low temperature MQL is 1.97%, 2.21% and 4.36% lower than that of pouring cooling lubrication. This shows that low temperature MQL cooling and lubrication can be used under high material removal rate.
2. Carbon emission during processing
Carbon emission index (CEI) during processing is an important parameter to measure the impact of different processing methods and process parameters on the environment. Therefore, the research on the influence of cooling and lubrication methods on carbon emissions during processing can provide important support for environmental protection agencies and relevant organizations to evaluate the performance of advanced cooling and lubrication auxiliary processing technology. The influence of cooling and lubrication methods and material removal rate on carbon emission indicators and their proportions are shown in Figure 9, where CEm represents carbon emissions from cutting, CEf represents carbon emissions from cutting fluid production, CECT represents carbon emissions from tool production, CEd represents carbon emissions from post-processing, CEMQL-oil represents carbon emissions from micro-lube production, and CELN2 represents carbon emissions from liquid nitrogen production. It can be seen from Figure 9 that under pouring cooling lubrication and low temperature MQL cooling lubrication (low temperature is provided by liquid nitrogen), the carbon emission index of the processing process decreases with the increase of material removal rate. The CEI under pouring cooling lubrication decreases from 0.538 to 0.167, while the CEI under low temperature MQL cooling lubrication decreases from 0.102 to 0.091, which not only changes slightly, but also is significantly lower than the value under pouring cooling lubrication, This shows that the cast-type cooling and lubrication method is not sustainable in terms of carbon emissions, while the low-temperature MQI auxiliary process is relatively clean and sustainable. In addition, under the pouring cooling and lubrication mode, the cost of the tool is high, and the carbon emission caused by it is relatively large; Under the low temperature MQL cooling and lubrication method, the carbon emission mainly comes from the production of liquid nitrogen. If the carbon emission caused by the production of liquid nitrogen can be improved through environmental protection production, the application prospect of the low temperature MQL cooling and lubrication method is more broad.
3. Comprehensive evaluation of the sustainability of cooling and lubrication technology
Based on the above analysis, it can be seen that the cooling and lubrication technology needs to be comprehensively evaluated and considered from the aspects of machinability, environmental protection, energy consumption and carbon emissions. However, for different processing objects, the impact of various cooling and lubrication technologies on various dimensions of sustainability is different, and the optimal processing parameters will not be consistent. The comprehensive evaluation is complex and needs to be determined according to the core needs of specific applications. From the perspective of sustainable development, the overall performance indicator (OPI) model and evaluation algorithm are established. Three cooling and lubricating methods, NFMQL, HNFMML and MQL, are analyzed with examples. In this assessment, the importance of different dimensions of sustainability determines the weight assigned to each indicator, that is, according to the importance of machinability, environmental protection, energy consumption and carbon emissions in specific applications, different weights are given to surface roughness, power and energy consumption, tool life, material removal, production costs and environmental and health impacts. The waste management part is regarded as a qualitative indicator.
Where, PI is the standardized performance index of a single research index of each cooling lubrication method; AP is the actual performance of each cooling and lubricating method; OP is the best performance; N represents the number of indicators studied.
Using the above evaluation methods, the sustainability evaluation results of AISI-1045 steel processed by three cooling and lubrication methods are obtained. The evaluation indexes are shown in the first column of the table. The PI is calculated according to the response value. It can be seen from that MQL shows the highest OPI (0.87), while for NFMQL and HNMQL methods, the OPI value is slightly lower due to the difficulties in the preparation process of nanofluids and the impact on the environment. However, this slight impact can be compensated if appropriate preparation methods are used and relevant waste management standards are followed. Therefore, HNFMML is still highly competitive.
