a four - station rotary thermoformer has a rotary carriage which transports a sheet of thermoplastic material clamped on a subframe through a load / unload station ; a heating station ; a forming station where the sheet is molded ; and a cooling station removed from the mold where the part is cooled on the subframe . the molded sheet is cooled in a cavity which has a lower portion mounted on a lift which travels vertically to engage against an upper portion and enclose the sheet for cooling . a multiplicity of air vents discharge cooling air into the cavity . cooling air leaves the cavity through recirculation duct . the supply of air within the cooling cavity results in a uniform current of air against the article &# 39 ; s surface , thus providing uniform cooling . a programmable controller controls the supply of cooling air and receives input from an infrared sensor which detects the temperature of the thermoformed article and also receives information from a sensor of the cooling air temperature . the programmable controller is programmed to provide a cooling cycle consisting of a three - parts . in the first part , the air is recirculated using the heat capacity of the recirculating air in the air supply system to start cooling at a low rate . during the second part , the flow of cooling air temperature is lowered until a pre - determined maximum cooling rate is reached and held for a selected time . during the third part , the cooling air is again recirculated .