PurposeThe purpose of the work presented in this paper is to capture the current state of Six Sigma as well as to document the current practices of Six Sigma through a systematic literature review so as to extend and update the previous work of Brady and Allen.Design/methodology/approachThe approach to this paper is to answer the questions such as “what is Six Sigma?”, “what are the applications of the Six Sigma?”, “what are the main enablers and barriers to its application?” and “what are the emerging trends?” These questions are used to guide the search of papers from various publication databases even if it is expected that existing literature might not be sufficiently developed to translate each question directly into a finding. The literature is then analysed and the major emerging themes are presented.FindingsSeven key findings (topics on which the views of the authors converged) and two issues (topics on which authors had differing views) have been established. These include the interpretation of Six Sigma, tools and techniques, implementation of Six Sigma, benefits, adoption, enablers and links to other disciplines.Originality/valueThe systematic literature review approach used in this paper allows emerging trends and issues in Six Sigma to be highlighted in a structured and thematic manner, enabling the future work to progress as Six Sigma continues to develop and evolve. The findings also open up new opportunities to apply Six Sigma in the fields that are not widely explored before for instance sustainability and product‐service systems.

This paper is concerned with the friction surfacing of high-speed steels, BM2, BT15 and ASP30 onto plain carbon steel plate. The events that the matrix and carbides experience as the coating material pass from the coating rod to the substrate, in forming the coating, is described. The coating is observed to harden automatically within a few seconds of being deposited onto the cold substrate. This autohardening is observed to be an inherent feature of the friction surfacing process and the only post-coating heat treatment required is tempering, as with traditionally hardened high-speed steels. The mechanism of autohardening is discussed in terms of the mechtrodercoatingrsubstrate thermal system. ᮊ

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The aim of this work is to identify relationships between the input variables and the process response and to develop predictive models that can be used in the design of new friction surfacing applications. Moreover to investigate the use of standard CNC machines for friction surfacing. The experimental design techniques and response surface methodology were used to investigate and select the combination of factor levels that produced the optimal response. The main effect of the velocity ratio obtained by dividing the feed rate of mechtrode with traverse rate of substrate was observed to be the most significant factor on the process response. Based on the results of optimisation it was observed that the lower to intermediate levels of rotational speed and intermediate to higher levels of velocity ratio produced good coating quality.