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Increasing miniaturisation has significantly increased demand for highly accurate small parts to be machined. Micro milling presents a viable method for series machining parts such as miniature heat exchangers or fuel injectors. Micro end mill tool wear, however, is considerably more difficult to monitor than its macro counterpart, and the tools often fail due to chipping or shaft failure. High tool breakage rates make costs unpredictable and machining times inefficient. Conversely, macro end mill wear is well characterised, and the typical wear curve well understood. The aim of this work is to elongate the steady state region (SSR) of the wear curve for micro end mills, as this is the practical life of the tool. Coatings can be applied to achieve this, improving wear rates and cutting performance. This study examines the wear that took place during straight-slot machining with 500 μm micro end mills. This was then compared with observed wear mechanisms on the macro scale. The length of the SSR was used to evaluate the ability of various new coatings to extend the working tool life. The relative predictability in the SSR allows tool paths to be modified to account for changing tool geometry. The results demonstrate that for micro-mills, the SSR could be elongated, in spite of less predictable wear mechanisms. Overall, this work presents a successful attempt to manipulate the wear curve for micro end mills and highlights the importance of developing an understanding of the wear mechanisms taking place for micro-mills as compared with macro-mills. • A comparison has been made between coatings for extending the tool life of micro-mills. • Wear curves are produced and wear mechanisms on both the micro and macro scale are investigated. • Specifically, the working useful life of the tool for each coating is considered, rather than simply tool life to failure. • Results show differences between wear mechanisms seen for micro and macro milling tools, giving an insight into coating design considerations. • The measure of working tool life gives a better indicator of quality of micro-mills. [ABSTRACT FROM AUTHOR]

This study presents novel results from in-situ stress relaxation tests using rubber O-ring seals immersed in bio-lubricant base oils (jojoba, soybean and palm oil), with a mineral base oil used for comparison. Little information is available on the interaction of bi-lubricants and elastomers. The use of Hanson Solubility Parameter modelling methods was considered for assessing compatibility. Some correlation was found between experimental results for EPDM. Results were inconclusive for NBR and FKM. EPDM immersed in palm and soybean oil suffered minor shrinkage, caused by stress relaxation. Swelling occurred with EPDM immersed in jojoba and mineral base oil, caused by diffusion. Results for nitrile showed shrinkage for all oils. Less than 1% change in mass occurred for all oils and FKM. • Stress relaxation tests and HSP analysis were used to assess the compatibility of bio base oils and common elastomer seals. • Jojoba oil and mineral base oil were incompatible with EPDM seals, with of swell of up to 23 and 38.5% respectively. • Plasticisers were readily extracted from NBR, resulting in seal shrinkage for all base oils tested. • Diffusion is driven by the molecular weight of the oils and level of unsaturated fatty acids in the bio-base oils. • Correlation of HSP and experimental mass change was observed with EPDM. • FKM and NBR are co-polymers which reduces the accuracy of HSP values. [ABSTRACT FROM AUTHOR]