Green machining of Ti6Al4V/Polymers composite made by pellets additive manufacturing

The poor surface finish (arithmetic roughness Ra around 40 µm) of additive manufactured parts leads to the development of hybrid machines to increase the quality of the final part in a lower production time. Hybrid machine already exists for DED (Directed Energy Deposition) and SLS (Selective Laser Sintering) but due to the hardness and the abrasiveness of the sintered material, important tool wear or surface defects on the workpiece can be observed. Therefore, reduced cutting parameters and dedicated cutting tool must then be used which increase the cost of machining operation and the time to produce a part. Green machining can limit these problems: the machining step is performed before sintering when the part does not have its final properties. This kind of material has a pseudo-plastic behavior so machining can be performed with high productivity thanks to lower cutting forces and reduced tool wear. An innovative use of the tool-material couple standard AFNOR Norm NF E66-520 (1999) dedicated to metals is proposed to determine the cutting parameters of a composite based on titanium alloys Ti6Al4V and polymers by measuring surface roughness and cutting forces. A tool dedicated to thermoplastic polymers was tested. Cutting forces and surface roughness (arithmetic surface roughness Ra and total surface roughness Rt) were evaluated for each test. Twelve sets of parameters considering the cutting speed vc, the axial depth of cut ap, the radial depth of cut ae and the feed per tooth fz as variables were tested. For the range of parameters selected, it is possible to achieve a satisfactory surface finish with low cutting forces (Ra remains close to 3.2 μm and cutting forces < 5 N) and stable results.