| Selective laser sintering(SLS)is an important material-adding manufacturing technology,which is widely used.Polymer material is the most widely used material in SLS technology.Ninety percent of commercial polymer powder materials on the market are polyamide12(PA12)and its composite powder.Polyamide6(PA6)has better mechanical properties and cheaper production costs than PA12,but it is difficult to apply to SLS process due to its high requirements for equipment.The purpose of this paper is to prepare PA6 and its composite powders which meet the requirements of SLS and make them become SLS materials with excellent properties.In this paper,PA6 powders were prepared by solvent method.The effects of dissolution temperature,stirring speed,nucleating agent and solvent ratio on the properties of PA6 powders were studied.The microstructure and morphology of PA6powders were analyzed by scanning electron microscopy(SEM)and X-ray diffraction(XRD).The melting temperature and crystallization temperature of PA6 powders were measured by differential scanning calorimetry(DSC).The results show that when the dissolution temperature is 160?,the stirring speed is 300rpm,the dosage of nucleating agent is 4.0wt%,the solute/solvent is 60g/L and the holding time is 30 min,the powder prepared has the best performance.The apparent density is over 0.45g/cm~3,and the powder with particle size in the range of 74-100um is over 80%.The sphericity of the powder is good,the crystallinity of the powder is 66.48%,and the sintering temperature window is 197.6-220.7?.In order to reduce the preheating temperature during sintering,a small amount of PA12 was added to PA6 in the process of solvent precipitation.DSC test results show that the sintering temperature window of composite powders was 184.1-216.4?,sintering temperature range was increased,which decreased the preheating temperature and increased the melt flow rate(MFR).PA6/PA12 composite powder was beneficial to SLS.The surface of Carbon fiber(CF)was treated by high temperature and mixed acid,and then was mechanically mixed with PA6 powder and injection moulded.The mechanical properties,morphology and thermal properties of the composites were tested.The results show that the two treatments have good interfacial bonding effect between CF and PA6,and CF can obviously enhance the mechanical and thermal properties of the composites.When acid treatment was used and CF content was30wt%,the comprehensive mechanical properties of PA6/CF were improved most appropriately.The increase rates of tensile strength,flexural modulus and impact strength were 26.8%,127.7%and 13.1%,respectively.When CF content was 50 wt%,Vicat softening point increased by 23.1?.Carbon nanotubes(CNT)were dispersed by surfactant method,alcohol dispersant method and aqueous solution method.PA6/CNT composite powder was prepared and then moulded by hot press.The mechanical properties,morphology and thermal properties of the composites were tested.The results showed that the alcohol dispersant method had the best dispersing effect on CNT.When the content of CNT is2.0wt%,the comprehensive mechanical properties of PA6/CNT are the best.The increase rates of tensile strength,flexural modulus and impact strength are 13.6%,31.4%and 58.0%respectively.The Vicat softening point increases by 17.5?.The surface of glass beads was treated with silane coupling agent and mechanically mixed with PA6 powder.The composite powder was sintered by SLS to analyze the mechanical properties and microstructure.The conclusion shows that the powder can be sintered when the laser filling power is 35W,the filling speed is 2000mm/s,the preheating temperature is 205?,the powder thickness is 0.1 mm and0.2wt%of the flow modifier is added.Increasing the glass bead content can enhance the mechanical properties of the parts.When the glass bead content is 30wt%,the tensile strength of the formed spline is 46.3 MPa,the impact strength is 7.69 k J/m,and the flexural modulus is 2976 MPa. |
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