Non Isothermal Tube Model Characterization for High Speed Thermoforming Stretch
Accurate non isothermal tube characterization reduces thermoforming wall variance to under six percent at hundred hertz stretch rates.
High Speed Sheet Stretch
Meaning
Rapid deformation behavior of thermoplastic sheets during thermoforming defines the limits of part wall thickness uniformity and cycle times. Analyzing high speed sheet stretch helps tooling engineers design molds that match the draw characteristics of specific resin formulations. This rapid stretching occurs in fractions of a second when vacuum or pressure is applied to the softened plastic sheet.
Deformation Mechanics
Extruded sheets experience biaxial elongation at high strain rates as they are forced into mold cavities. During high speed sheet stretch, the polymer molecules must untangle and align without tearing or creating localized thin spots. The temperature of the sheet must be controlled within a narrow window to balance the melt strength against the mechanical force of the forming system.
Material Impact
Different grades of resin behave uniquely under rapid elongation due to variations in molecular weight distribution and branching. Incorporating recycled content often reduces the allowable high speed sheet stretch because regrind has shorter polymer chains that offer less resistance to thinning. Moulders must adjust the speed of the forming plugs to accommodate these material limitations and prevent part blowouts.
Process Optimization
Reducing cycle times in high-volume packaging lines requires maximizing the speed of the forming process. Measuring the high speed sheet stretch limits of a material allows processors to run machinery at peak rates without risking defect spikes. These data are used to fine-tune the heater bank settings, ensuring that the sheet is heated evenly across its entire width before entering the forming station.
This thermal uniformity prevents the sheet from stretching unevenly, which would otherwise result in thin corners or inconsistent flange thickness on the finished trays.