INFLUENCE OF BINDER CONTENT AND PARTICLE-SIZE ON GREEN STRENGTH OF WPP PARTS

Wet powder pouring (WPP) was developed as an alternative near net shap e process to metal injection moulding (MIM). The amount of binder, whi ch is necessary to obtain a sufficient green strength, is relatively l ow (2-5 vol.-%) compared to the amount used in the MIM process (about 30 vol.-%). This is advantageous with respect to short debinding times and low residual carbon and oxygen contaminations. A further reductio n of the binder content or the application of the WPP process to new m aterials would be promoted by an understanding of the dependence of gr een strength on particle characteristics and binder content. In the pr esent investigation the green strengths of stainless steel WPP parts w ere determined for different particle size distributions and different binder contents (2-8 vol.-%). The green strength was in the range 3 t o 7 MN m-2 and the fracture mode was always brittle. A simple fracture mechanical model was developed, which was able to explain the observe d relations between binder content, particle size, and green strength.