Role of Adhesive Properties in Incremental Forming of Adhesive Bonded Steel Sheets and a Strategy of Improving Forming Quality of Sheet Metal

Incremental forming of steel sheets bonded with adhesive with the effect of properties of adhesive is experimentally investigated. Also, the strategy of improving the forming quality of the sheet metal by selecting suitable adhesive properties is demonstrated. Drawing quality cold rolled steel sheet of 0.6 mm thickness as a face sheet and a two-part epoxy adhesive system were used for fabricating bonded sheets with adhesive. The properties of adhesive were modified by varying the hardener-to-resin ratio. Two types of bonded sheets with adhesive namely two-layer (steel/adhesive) sheet and three-layer (steel/adhesive/steel) sheet were fabricated. In addition, the two-layer and three-layer sheets were formed without interface bonding of the adhesive layer with face sheets, and compared with the formability of bonded sheets. Truncated conical cups made of bonded sheets, single sheet, and double sheet (steel/steel) were formed by the single-point incremental forming process. Failure pattern and cup height were monitored, and strain distribution, thickness distribution, and limit strain of the face sheets constituting bonded sheets were evaluated. It is found that the hardener-enriched adhesive helps improve both local plastic strain and the total formability of steel sheets bonded with adhesive. The absence of interface bonding of the adhesive layer with face sheets reduces the formability of face sheets. The hardener-enriched adhesive layer stacked under the steel sheet without interface bond offers a cushioning effect during the forming process and helps improve the formability of the steel sheet.