Thermoformer

A thermoformer molds shapes into a plastic sheet (fed in sections, from a roll, or inline from an extruder) using a combination of heat, and both positive and negative air pressure.

Sheet is indexed between two mold sections - one with tooling called plugs imparting the positive shape, and the other containing "negative" cavity tooling. The type of product determines which mold section contains plugs versus cavities - for cups, cavities are in the top, and plugs mounted in the bottom platen, while for lids it is usually visa-versa. Positive air pressure pushes heated plastic sheet from the plug side of the mold, and vacuum "sucks it up" towards the cavity. The cavity size is usually water cooled using a TCU (Temperature Control Unit) to maintain a consistent temperature, and (though quicker cooling) allowing faster machine cycle times.

This may sound simple, and at this level of abstraction it is. However, in the real world thermoforming is just now moving from 'black art' to a sound scientific standing.

A typical thermoformer may be equipped with an '81 up' cup tool with a matrix of 9x9 plug/cavity sets in a 50" square tool, pressurized at 40 PSI, and run with a cycle time of 4 seconds. This means (for a 24 hour/day operation with a machine utilization of about 85%) the former will cycle about 6.7 million times per year, and produce more than 540 million cups. A 50 square inch tool at 40 PSI of air pressure needs to operate at 50 tons of force, so one might imagine how much of a beating the typical former must endure.

Trimpress

Once the thermoformer has molded parts into the sheet it is passed to the trimpress, which cuts out the desired parts and moves them to a takeoff tray, and drops the scrap pieces into a grinder so they can be made available for reuse.

The press is equipped with a set of punches and dies with as many columns as there are columns in the former, and rows in multiples. For instance, the 9x9 former mold tool may use a press equipped with one or three row tooling. At a form time of 4 seconds (or 15 cycles per minute) a single row tool needs to make 9 cuts per former cycle, or run at about 135 RPM, which will either be at or beyond the speed limit of most trimpresses. This is why a three row press tool makes more sense - trimpress speed can be a more survivable 45 RPM.

Created and maintained by Bob Welker for his own personal amusement. All trademarks, and so on that appear belong to their respective owners. None of the information contained within is guaranteed in any way.