The invention relates to a method for manufacturing a one-step formed composite foamed plastic formwork which comprises an upper
surface layer, a lower
surface layer and a core layer. The method comprises the following steps of: firstly, filling a core layer
raw material into a high-speed mixing
machine to perform mixing; secondly, sending the mixed core layer
raw material into a double-screw extruder by a feeding
machine, extruding the extruded material into a core layer extruder, and simultaneously sending
surface layer raw materials into a plastic extruder; and thirdly, extruding the extruded core layer
raw material, the upper surface layer raw material and the lower surface layer raw material into a confluence
distributor, molding the materials in a mold, and performing three-roller press finishing or vacuum shaping, cooling and
cutting to obtain a finished product. The method overcomes the defects that the plastic formwork has rigidity and tenacity; the plastic formwork can be extruded out with three
layers or a plurality of
layers and has a more reasonable structure; the middle part of the plastic formwork is a foam material; the weight of the plastic formwork is light; the plastic formwork plays a role in heat insulation and simultaneously reduces the abuse of large heat
shrinkage rate of plastic, can be recovered for 100 percent, has more turnover times, high rigidity,
cold resistance, high
temperature resistance,
corrosion resistance, acid and alkali resistance, easy demoulding and low production cost; besides, the plastic formwork can be customized to be made into any sizes, has fewer building wallboard seams, and has the advantages of making a wall body smoother and evener, saving more materials and the like.