Design And Implementation Of 3D Printer For Small High Density Polyethylene Ship Hull Construction

With the implementation of the national“marine power”strategy and the emphasis on promoting high-end,intelligent and green manufacturing of traditional industries,developing strategic emerging industries,and accelerating the development of eight new technologies,including marine equipment and high-end equipment,in the national“Fourteenth Five Year Plan”,shipbuilding should achieve certain technological reform,focusing on intelligent and green manufacturing.If the 3D printing technology,one of the intelligent manufacturing technologies,is applied in the field of small ship construction to achieve rapid printing of small ships,it will greatly promote the innovation of the traditional hull construction mode.There are two limitations in the application of 3D printing technology in the field of ships:one is printing materials;The second is printing equipment.High density polyethylene（HDPE）has the advantages of high specific strength,low density than water,friction resistance,corrosion resistance and low notch sensitivity.At present,small high-density polyethylene ships are being used in China,and the country has issued relevant policies and regulations to regulate the construction and use of high-density polyethylene ships.Applying high-density polyethylene materials to 3D printing can solve the problem of inapplicability of ship building materials,and realize the further development of3D printing technology in the field of small ship manufacturing.First,the fused deposition（FDM）3D printing process is selected,and high-density polyethylene is used as the 3D printing material According to the forming principle of 3D printing,combined with the characteristics of large hull size and long printing forming time of small ships,the printing platform is fixed and the nozzle moves in three directions.Then the gear rack is selected as the transmission system to complete the design and calculation of the gear;Further select and complete the design and calculation of the main parameters of the screw of the extrusion system,and calculate that the maximum pressure when high-density polyethylene particles enter the screw is2.55×10^-3Mpa;Finally,the construction of 3D printer is completed.Its printing range is infinite（theoretically）in length,7000mm in width and 2000mm in height.Secondly,the basic laws followed by the polymer melt and the viscoelastic constitutive equation of non Newtonian fluid were analyzed.Three 3D printing process influencing factors,namely,screw extrusion amount,nozzle die inner diameter and convergence angle,were selected to design an orthogonal experiment.With the help of Polyflow software and range analysis,it was found that the biggest factor affecting the flow speed and temperature of high-density polyethylene melt was the die inner diameter,followed by the extrusion amount,and finally the convergence angle,In combination with the construction of small high-density polyethylene hull,the best 3D printing process scheme is selected,with the extrusion amount of 2cm³/s,nozzle inner diameter of8mm,and convergence angle of 150°.Finally,combined with the research results of mechanical properties of plastic test pieces,tensile tests were conducted on high-density polyethylene test pieces manufactured by 3D printing.The test results met the requirements of national standards.At the same time,printing of small high-density polyethylene hull was carried out.According to the characteristics of the hull,different printing methods were designed to continuously optimize the hull structure,and printing of small high-density polyethylene hull was completed.As a very important part of ship building,optimizing the hull structure on the basis of 3D printing can promote the further application of 3D printing in the field of ship building,and 3D technology is gradually developing towards large-scale,which is more suitable for the model of ship building,and can realize the technical innovation of traditional ship building model,It is of great significance to promote the intellectualization of the traditional shipbuilding industry in the national development strategy.