Forming Limit
Extensibility threshold parameters define the maximum planar elongation a virgin paperboard substrate can undergo before microscopic fibre bond rupture occurs during deep drawing strain. Converting lines experience structural failure on the shoulder radius if press tonnage exceeds the internal tear resistance of the multi-ply sheet. Press operators adjust blank holder pressure to govern material flow into the die cavity, preventing premature cracking along vertical sidewalls.
Die radius geometry dictates stress distribution across the circular blank, restricting how sharply a tool can bend without delaminating the inner coating layers. Rigid packaging containers require continuous monitoring of moisture content because dry wood pulp loses the elasticity necessary for deep drawing strain without fracturing under high compression loads.
Process Tolerance
Press speeds and die clearance gaps determine whether commercial blanks achieve uniform caliper reduction during the shaping phase. Tooling engineers calculate springback compensation angles to counteract the elastic recovery exhibited by cellulose fibres once mechanical clamps release the finished tray. Production facilities maintain temperature controls in the forming room because thermal variance alters the residual moisture within heavy packaging boards, shifting failure thresholds unpredictably during continuous shifts.
Die sets demand periodic polishing to eliminate micro-scratches that create localized friction points, which tear thin barrier coatings applied to food container stock.
Material Yield
Tensile strength values derived from cross-directional laboratory testing establish the baseline performance expected from virgin kraft liners before they reach stamping machinery. Paper mills certify burst index ratings to guarantee that specific batches withstand the multi-axial tension generated by deep drawing strain without bursting at the base corners. Supply contracts specify allowable caliper variance because over-caliper stock jams pneumatic feeding mechanisms, whereas under-caliper stock produces pinholes in finished thermoformed blisters.
Final quality audits measure sidewall thickness uniformity to verify that the forming process maintained adequate barrier integrity across the entire surface area of the packaging component.
