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.
Plug Assisted Thermoforming
Meaning
Mechanical pre-stretching of heated thermoplastic sheets using a forming plug improves the wall thickness uniformity of deep-drawn containers. Implementing plug assisted thermoforming allows packaging manufacturers to produce lighter cups and trays while maintaining structural strength in the corners. This process is used extensively in high-speed packaging lines for food and medical products.
Mechanical Action
Solid plugs push the softened plastic sheet into the mold cavity to distribute the material before air pressure is applied. During plug assisted thermoforming, the material of the plug, its temperature, and its descent speed must be controlled to prevent the sheet from sticking or cooling too quickly. Nylon or syntactic foam plugs are chosen because they minimize heat transfer from the plastic.
Thickness Distribution
Uneven stretching of heated sheets can lead to thin corners that fail under load or during storage. By using plug assisted thermoforming, processors can force more material into the bottom and sides of the mold cavity. This redistribution produces parts with more uniform walls, which means that less starting plastic is needed to achieve the required structural performance.
Process Variables
Controlling the timing between the plug movement and the vacuum application is necessary to avoid defects like drag marks or wall thinning. In a typical run, the plug must reach its full depth just as the forming air or vacuum begins to pull the sheet against the mold walls. Small errors in this timing can cause uneven cooling, leading to warped flanges and rejected batches of finished containers.
This synchronization is set on the machine controller and must be adjusted whenever there are changes in resin grade or sheet thickness.