Meaning
Resistance to sliding that occurs between the heated plastic sheet and the mechanical tool used to push the material into a mold cavity dictates how the polymer stretches during thermoforming. Controlling plug assist friction is necessary to achieve uniform wall thickness in deep-drawn parts. This interaction is influenced by the material of the plug and the temperature of both the tool and the sheet.
Sheet Stretching
Friction forces prevent the plastic sheet from thinning excessively where it first contacts the plug. When the sheet is gripped by the plug, it is pushed deeper into the cavity before stretching begins, which improves the material distribution.
Tool Material
Selection of the proper plug material alters the traction between the sheet and the tool. Polytetrafluoroethylene or syntactic foam plugs provide low thermal conductivity and controlled friction, preventing the plastic from freezing prematurely.
Thickness Distribution
High friction can cause the sheet to stick to the plug and create thin areas on the sidewalls of the formed part. If the sheet slips too easily, the material accumulates at the bottom, so maintaining the correct friction level is necessary to balance the distribution of the plastic between the bottom and the sides of the finished component during high-speed production runs.
