Study On Insert Injection Molding Process Based On 3D Printed Mold

As a main processing method of batch processing thermoplastics,injection molding has been widely used in many industries such as transportation,electrical appliances,medical treatment,packaging.However,the traditional molds required for injection molding have complex processing procedures and high preparation costs,and are only suitable for mass production of mature products.In recent years,with the maturity of 3D printing technology,the use of 3D printing to fabricate rapid molds for small batch production has gained more and more attention.Among 3D printing technologies,Stereo Lithography Appearance(SLA)has the highest accuracy and efficiency,and can be used for the preparation of injection molds.However,the photosensitive resin used in SLA is mainly a variant of acrylic or epoxy resin,and its material characteristics are very different from those of metal.The impact of mold material characteristics on the injection molding process and product quality is still lacking in detailed research.On the other hand,insert injection molding has important applications in the production of functional devices.However,the impact of melt during insert injection molding in traditional molds can easily cause deformation of thin-walled inserts.Therefore,this thesis intends to use SLA-prepared light-curing molds for insert injection molding,using the low thermal conductivity of light-curing molds to reduce the injection speed and injection pressure,and solve the problem of insert deformation caused by the melt impact in the traditional mold injection process.At the same time,through simulation analysis and experiments of injection molding processes,the influence of light-curing molds on the roughness and the warpage caused by shrinkage of injection molded products is determined.The detailed research contents are as follows:(1)Nylon 66(PA66)containing 33% glass fiber is selected as the injection molding material,and the differences of melt curing process in metal cavity and that in light-curing cavity are identified by simulation using Moldflow.Because of the high thermal conductivity of metal material,the material on the cavity surface solidifies quickly,the orientation of fiber on the product surface is cluttered during injection molding and the roughness of the product surface is affected when the fiber floats on the product surface.Nevertheless,the heat conductivity of the light-cured mold is lower than metal material so the melt solidifies in the mold cavity for a longer time and the fiber can be oriented along with the flow of the melt,which is helpful to improve the surface quality of injection molded products.(2)The influence of injection speed on the roughness and the insert deformation of the molded PA66 products is studied.Increasing injection speed can improve the surface roughness of injection molded products,but the injection pressure is higher when the injection speed is increased,and melt filling will cause insert deformation.When the injection speed of metal mold is increased to 40mm/s,PA66 substrate can wrap fiber,but the injection pressure required at this time is 75 MPa,and the insert diameter deformation caused by injection pressure is as high as 78.4?m.The PA66 substrate can be coated with fibers when the light-curing mold is injected at a speed of 10mm/s,the corresponding injection pressure is50 MPa,and the insert diameter deformation can be reduced to less than 10?m.The heat conduction characteristics of the light-curing mold can avoid insert deformation caused by the injection molding process on the basis of ensuring the surface quality of the injection molded product.(3)Low density polyethylene(LDPE)with low melting temperature was selected as injection molding material,and the influence of heat conduction characteristics of light-curing mold on shrinkage and warpage of injection molding products was studied.When the injection molding process is the same,due to the slow heat dissipation of the light-curing mold,the crystallinity of the molded product is higher than that of the metal mold,the shrinkage of the injection molding material increases after crystallization,and the warpage caused by uneven shrinkage of the product also increases.Through simulation analysis and orthogonal experiment,it is concluded that melt temperature,holding pressure and holding time are the main processes that affect the shrinkage of injection molded products.Reducing melt temperature and increasing holding pressure and holding time can reduce the shrinkage of molded products.After process optimization,the dimensional accuracy of light-curing mold injection products can reach the level of metal mold molding.