Conclusion

This thesis has investigated the link between punch force signature variation and galling wear progression in deep drawing of sheet metal parts. This work has specifically addressed the problem statement (Section 1.2) and research objectives (Section 1.4). To conclude this thesis the significance and place of the work in the field will be discussed, the key contributions will be summarised, and avenues for further investigation will be recommended.

9.2Summary of contributions

This work has made a number of contributions in the process of addressing the specific research objective outlined in Section 1.4. The contributions of this thesis build on and advance the fields of sheet metal stamping process signal analysis, process monitoring, and galling wear severity quantification. A new methodology for quantification of galling wear severity has been presented that illustrates a novel approach in targeting specific surface features. The new measure provides an accurate measure of galling wear severity for the use in developing wear monitoring systems as well as assessment of wear in industrial settings. The thesis also provides insight into the effects of galling wear and other friction conditions on the variation of punch force signatures. These insights provide a foundational understanding that can assist with the development of wear monitoring systems in sheet metal forming, a tool that will address the significant issue of tool wear in sheet metal forming

148

industries. The details of each of these contributions are summarised with respect to the research objectives of the thesis.

Objective: Determine if variation in wear and other friction influencing factors have a demonstrable effect on punch force signatures (Chapter 4).

• Punch force signatures from channel forming trials were found to be clearly affected by changes in galling wear severity on tooling, changes in lubricant type, and changes in BHF level.

• PCA of punch force signature data sets were shown to be an effective tool for isolating the effects of changes in wear and other friction conditions.

• A number of common general forms of signature shape variation were observed in the analysis of 2 punch force signature data sets focusing on variation of wear severity, and variation of other friction influencing factors. Two specific forms of signature shape variation allowed for distinction between signatures collected under different wear severities, lubricants, and BHF levels.

Objective: Develop an accurate method for quantifying galling wear severity that can be applied to channel forming experiments conducted in this work (Chapter 5).

• A new methodology for quantifying galling wear severity was presented in the form of the DWT methodology.

• The DWT methodology has a number of features that make it suitable for use in the channel forming experiments and also make it more accurate than alternative measures.

• The methodology uses Discrete Wavelet Transformation to target galling wear features in 2D surface profiles of the die counter surface, and no other galling wear measure aims to target galling specific features.

149

• The methodology provides an indication of the location and relative severity of localised galling wear damage in the form of detail coefficients, and a parameter that quantifies the overall severity of galling wear severity on the surface in 𝑊_𝐷𝑊𝑇.

• The methodology was shown to provide an accurate quantifiable measure of galling wear severity in galling initiation and galling progression cases.

Objective: Examine if the onset and progression of galling wear has a quantifiable relationship with punch force signature shape variation (Chapter 6).

• The PCA of punch force signatures for extended channel forming trials in which galling wear progressed in severity has been presented. These wear trials demonstrated a progression of galling wear severity in two forms, continued increasing severity and plateaued severity.

• In the extended channel forming trials conducted, galling wear severity progression was found to have a strong linear relationship with punch force signature magnitude.

• In the same trials, peak punch force was also found to have a relationship with galling wear severity progression, however, not as strong as the relationship seen with punch force signature magnitude.

• The slope of the punch force signature plateau was not found to have a conclusive linear relationship with galling wear progression in both test trials.

Objective: Investigate how specific wear events and changes in friction influencing factors affect the punch force signature (Chapter 7).

• Using experimentally determined coefficients of friction for lubricant types the magnitude PC is linked to the coefficient of friction between the tooling and blank.

150

• This correlates well with theory relating to the effects of wear and blank holder force on friction, as well as observations from the trials conducted.

• The slope of the punch force signature plateau or the progression of the punch force was linked to the lubrication mechanism change experienced near the end of the stroke. Such a mechanism change is characterised by the lubricant film thinning, changing from a mixed lubrication regime to boundary lubrication or even dry contact as film thickness reduced.

• The slope of the punch force signature plateau or the progression of the punch force was qualitatively linked to changes in the dominant type of wear damage in galling wear tracks, either adhesive or abrasive wear damage.