Hybrid Incremental Forming: Investigation on Localized …
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reduction as compared to thinning band is observed near apex of cone. Thickness
reduction takes place according to hemispherical bulging as discussed in Sect. 2.2 and
is identical to thickness distribution reported by Santos et al. [23]. Hence, minimum
thickness reduction at thinning band and uniform thickness distribution along formed
surface are obtained using 10 mm preforming depth.
3.2 Influence of Tool Shape on Thinning and Thickness
Distribution
As discussed in the previous section that preforming using 10 mm stretching results
in slight enhancement in the thickness distribution and thickness reduction at thinning band. The preforming process also accounts for the thickness reduction near
the apex of conical frustum which leads to uneven thickness distribution. As the
shape of preforming tool is hemispherical, thickness reduction in the first stage of
preforming follows hemispherical bulging. According to the hemispherical bulging
process, maximum thickness reduction takes place at the centre of hemispherical
bulge as discussed in materials and methodology Sect. 2.1. Hence experimental
investigation on the influence of preform tool shape is carried out to optimize the tool
shape in order to improve thickness distribution and localized thinning. In previous
experiments, preform tool having a radius of 50 mm is used. Hence, more tools
are designed using preform tool radius as shape function as depicted in Fig. 5. Full
factorial design of experiments (DoE) plan is used for planning the experimental
campaign.
Experiments are carried out to rectify the influence of preform tool shape in
terms of preform tool radius and stretching amount using full factorial design of
experiments plan. Table 4 gives the process parameters and their levels.
Result of the full factorial experiments is analyzed using ANOVA at 95% confidence interval. The ANOVA table shows the variability of preform tool radius
and preforming depth on thickness (T min ). Table 5 is ANOVA table for minimum
thickness using full factorial design of experiments plan.
Fig. 5 Wooden preforming tools having radius of 50 mm, 70 mm and 90 mm respectively
157
reduction as compared to thinning band is observed near apex of cone. Thickness
reduction takes place according to hemispherical bulging as discussed in Sect. 2.2 and
is identical to thickness distribution reported by Santos et al. [23]. Hence, minimum
thickness reduction at thinning band and uniform thickness distribution along formed
surface are obtained using 10 mm preforming depth.
3.2 Influence of Tool Shape on Thinning and Thickness
Distribution
As discussed in the previous section that preforming using 10 mm stretching results
in slight enhancement in the thickness distribution and thickness reduction at thinning band. The preforming process also accounts for the thickness reduction near
the apex of conical frustum which leads to uneven thickness distribution. As the
shape of preforming tool is hemispherical, thickness reduction in the first stage of
preforming follows hemispherical bulging. According to the hemispherical bulging
process, maximum thickness reduction takes place at the centre of hemispherical
bulge as discussed in materials and methodology Sect. 2.1. Hence experimental
investigation on the influence of preform tool shape is carried out to optimize the tool
shape in order to improve thickness distribution and localized thinning. In previous
experiments, preform tool having a radius of 50 mm is used. Hence, more tools
are designed using preform tool radius as shape function as depicted in Fig. 5. Full
factorial design of experiments (DoE) plan is used for planning the experimental
campaign.
Experiments are carried out to rectify the influence of preform tool shape in
terms of preform tool radius and stretching amount using full factorial design of
experiments plan. Table 4 gives the process parameters and their levels.
Result of the full factorial experiments is analyzed using ANOVA at 95% confidence interval. The ANOVA table shows the variability of preform tool radius
and preforming depth on thickness (T min ). Table 5 is ANOVA table for minimum
thickness using full factorial design of experiments plan.
Fig. 5 Wooden preforming tools having radius of 50 mm, 70 mm and 90 mm respectively