**3.5. Conclusion**

The cost-effective and sustainable manufacturing techniques are being given considerable importance these days to ensure economic, societal, and environmental sustainability globally. The basic parameters of nanofluids are discussed in detail, and they give strong effects on their tribological and lubricating characteristics, as well as the cost of NFs. The selection of appropriate nanofluids with suitable parameters is the crucial factor for machining processes. Especially for hard machining materials using geometrically defined cutting edges (hard turning, hard milling, hard drilling, and so on), the effectiveness of nanofluids is evaluated in terms of reducing the friction coefficient, enhancing the cutting performance, ensuring the tool life, and achieving good surface quality. However, very few records can be seen in the literature indicating that more experimental research is needed to find the optimal parameters in order to ensure maximum performance of using nanofluids in machining.
