| The Vacuum Molding Process(V-Process)can form castings with high dimensional accuracy and excellent surface quality,the comprehensive cost is low,which is gradually gaining more and more attention at home and abroad.In foreign countries,at present,V-Process casting technology of light metal alloy(mainly aluminum alloys)has been relatively mature,and its products are mostly used in medical,electronics,communications and other industries,while in China,the V process is mainly applied to forklift counterweights,axles and other gray iron parts,cast steel parts,ductile iron parts,etc.,which have low surface quality and dimensional accuracy requirements,V-Process casting technology of aluminum alloy has not been promoted.Therefore,it is of great significance to conduct in-depth research on key process parameters and process equipment in V-Process of aluminum alloy.In this paper,the possibility of FDM(Fused Deposition Modeling)printing V-Process modeling die is studied firstly,the results show that the hardness of the FDM printed PLA(Polylactic Acid)material die is 80-84 HD,which is higher than the hardness of the wood die;the compression yield strength σs≥33.8702 MPa,the elastic modulus E≥ 1.3834GMPa;the volume shrinkage is 0.52-1.24%,which is lower than the shrinkage of wood(pine)when it loess 1% water,which is close to the free shrinkage of aluminum alloy die;the surface roughness of the die is 1.5-4.0 μm,which is lower than the epoxy resin die by CNC and the wooden die without putty.At the same time,the paper also studied the effect of filling rate and die top/bottom thickness on the properties of FDM printing V-Process modeling die(mechanical properties,dimensional accuracy,surface roughness,etc.),the study found that the compressive yield strength and elastic modulus of the die increase with the increase of filling rate and top/bottom thickness,and the filling rate is promoted to be stronger than the top/bottom thickness;the surface roughness of the die decreases as the filling rate increases;in terms of volume shrinkage,an increase in the filling ratio or a decrease in the top/bottom thickness can contribute to a reduction in die volume shrinkage.FDM printed PLA material die meets V-Process modeling requirements.Secondly,the distribution of vacuum degree in V-Process mold and the distribution of temperature field in mold,interface of casting-mold and internal casting in the process of pouring and solidification of aluminum alloy,the results show that for the same type of sand,when the sensor is the same depth from the back side of the V-Process mold,the vacuum degree near the edge of the flask is higher than the vacuum at the geometric center of the mold X-Y plane,but the difference between the two is not large,in the range of 0.001-0.002 MPa.When the depth of the sensor into the mold changes,the change trend of the vacuum degree varies with the different sand.In the silica sand and 100 mesh orb sand molds,the vacuum degree decreases first and then increases with the increase of the depth of the sensor inserted into the mold,but does not rise to the value before the reduction.In the chrome ore sand and 140 mesh orb sand molds,the vacuum degree gradually decreases with the increase of the insertion depth of the sensor into the casting mold,and reaches the lowest value at a depth of 150 mm from the back of the mold.In the 200 mesh orb sand mold,the vacuum degree is relatively stable,and it hardly changes with the change of the depth of the sensor into the mold.The distribution of vacuum in the chrome ore sand mold is more uniform than that of the silica sand.Among the three types of orb sands,100 mesh,140 mesh,and 200 mesh,the vacuum distribution of the 200 mesh orb sand mold is the most uniform,and the vacuum distribution of the 140 mesh orb sand mold is the most fluctuating.The addition of the die will increase the overall vacuum of the V-Process mold by 0.0001 MPa to 0.0015 MPa(relative to the die-free mold),but will not affect the distribution characteristics of the vacuum in the V-Process mold.In terms of temperature field distribution,the cooling rate of aluminum alloy castings in chrome ore is significantly higher than that of orb sand and silica sand,while the cooling rate of orb sand is slightly higher than that of silica sand.The steps of aluminum alloy castings have the shortest solidification time in the chrome ore mold,the secondary dendrite arm spacing is the smallest,and the cooling rate is the highest.In the orb sand mold the solidification time is less than that of the silica sand,and the secondary dendrite arm spacing is approximately equal,that is,the cooling rate of the aluminum alloy casting in the orb sand mold is slightly higher than that of the silica sand. |
