a control process for foaming and fusing plastics in a foaming and fusing device , and a fusing device for carrying out the process , in which the control process works in cycles , each cycle consists of phases which are at least an injection phase , a heating phase , a fusion phase , a cooling phase and a mould release phase , such phases being started and completed depending on control criteria comprising a time period , a pressure or a temperature limit value for the conditions evolving in the device such control criteria belonging to a certain cycle comprising a control criteria set , and with each cycle quality values of predetermined characteristics determined by measurements taken from the respective plastic part or an agglomerate cake situated in the device , a new set of control criteria being generated for each new cycle from prior control criteria depending from the quality values measured with such prior cycle of the control process , wherein the quality values of each cycle are combined to a deviation which deviation together with the control criteria set of the respective cycle are stored in a control device store up to a predetermined number of such stored sets , and criteria averages are determined from each of the store control criteria and an average of the stored quality deviations is determined , and for each cycle a new set of control criteria is determined through statistical variations of one or more of the control criteria around their criteria average with a variance determined according to the average quality deviation , such new set of control criteria is preset for the control of the next working cycle and the related quality values and the deviation is determined which is compared to the stored deviations and if it is smaller than one of the stored deviations , the set with the largest deviation in the store is replaced by the new one .