Life analysis of coated tools using statistical methods

S. J. Dowey, J. Zhang, E. D. Doyle, A. Matthews

Research output: Contribution to journalConference articlepeer-review


The lifetime improvements achieved using physical vapour-deposited (PVD) TiN on hexagonal washer punch tools used in the fastener industry have been investigated. Tools were coated with PVD TiN initially in an unmodified form and later with surface preparation changes prior to coating. An original analysis, relying mainly on the visual appraisal of scanning electron micrographs and a rudimentary study of the lifetime data, found that the failure modes of the tools were altered by modifying the tool manufacturing process as well as by applying a surface coating. Sample mean lifetime of the best tools was over six times that of the mean sample lifetime of the unmodified, uncoated tools. By retrospectively applying experimental design techniques to the data, the influence on the lifetime from the tool modifications and the coating application have been decoupled. This shows that the tool modifications produce a larger lifetime response than the presence or not of a PVD coating. However, the interaction of the PVD coating and the tool modification produces a stronger positive response. Simple visualisation techniques have been used to effectively present this information in the form of ANOM (analysis of means), response charts, box plots and scatter diagrams. A three-parameter Weibull analysis also revealed evidence to suggest that, as well as different failure modes between treatments, some treatments underwent a number of early life failures by different failure modes. This is revealed purely from the distribution of the data and as such greatly enhances the visual analysis and interpretation of the previous analysis. The characteristic life for the improved tooling in this particular case is 465 200 operations as opposed to 72 000 for the original tooling. This study highlights the benefits of a full statistical analysis in assessing the benefits of coatings on production tooling, especially where the use of a coating is coupled with other changes in tool design and preparation.

Original languageEnglish
Pages (from-to)654-661
Number of pages8
JournalSurface and Coatings Technology
Publication statusPublished - 1 Sept 1999
EventProceedings of the 1998 6th International Conference on Plasma Surface Engineering (PSE-98) - Garmisch-Partenkirchen, Ger
Duration: 14 Sept 199818 Sept 1998


  • Experimental design
  • Forming tools
  • TiN
  • Weibull


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