This paper highlights the machinability of primary recycled thermoplastics as workpiece (WP) material with secondary recycled (reinforced) thermoplastic composites as rapid tooling (RT). Both WP and RT have been 3D printed on commercial fused deposition modelling. For investigating machinability of primaryrecycled thermoplastics, un-reinforced WP of low-density polyethylene (LDPE) and high-density polyethylene (HDPE) has been selected. The RT materials were secondary reinforced (recycled) LDPE with double particle size Al₂O₃ particles and HDPE with triple particle size Al₂O₃. The machinability has been calculated in terms of weight loss of WP, while machining on a vertical milling set-up. This study also reports the surface hardness, porosity, surface roughness (Ra) and photomicrographic observations of WP and RT under controlled machining conditions. Further thermal analysis suggests that primary recycled thermoplastic can be successfully machined with secondary recycled RT, resulting in improved thermal stability and surface properties.

The virgin thermoplastics have numerous applications in fused deposition modelling (FDM) process. Commercially, different thermoplastics are recycled through extrusion (without any reinforcement as primary (1^°) recycled materials) for enhancing their reusability and sustainability. However, hitherto very littlehas been reported on mechanical and thermal properties of cryogenic (cryo) milled 1^° recycled ABS (to be used on FDM-based 3D printer). In the present research article the cryo ball milling of 1^° recycled ABS thermoplastichas been reported to explore the influence of cryo environment (-196 ^°C) on mechanical, thermal and surface properties of the ABS-based feed stock filament (prepared through screw extrusion) for further use on commercial FDM set-up (without any hardware/software change). The process parameters of cryo-milling (like frequency of vibration, milling time and grinding media weight) have been selected for investigations using Taguchi-based design of experiment (DOE). The study results show significant improvement in peak strength (PS) of the cryo-milled ABS in comparison with non-cryo-milled ABS without any degradation of thermal properties (mainly heat capacity). As regards the process parameters of cryo-milling, 30-Hz frequency, 15-min milling time and 32-g media weight are the best settings for maximum PS. The maximum value of PS observed was 61.32 MPa. The optical photomicrographs supported with 3D rendered images were captured to support the surface characteristics and porosity level in the wires (to be used as feed stock filament for FDM) prepared with cryo-milled ABS (powder samples).