Experimental and finite element simulation study of capsule-free hot isostatic pressing of sintered gears
A novel approach to reach full density in powder metallurgy (PM) components is demonstrated in this work. Water-atomised Mo-prealloyed steel powder is utilised for manufacturing cylindrical and gear samples through double pressing and double sintering (DPDS) process route. The effect of sample geometry and powder size fraction on densification is investigated and it is found that the DPDS route enables a density level of > 95% which is sufficient to eliminate the surface open pores. Reaching such high density is necessary, in order to perform capsule-free hot isostatic pressing (HIP). After HIP, full densification is achieved for the cylindrical samples and only near full density is realised for the gears resulting in neutral zone formation due to the density gradient. In order to predict the densification behaviour during the compaction, FEM simulations considering the gear geometry are performed for both the pressing stages and HIP. The simulation predicted a similar densification behaviour with the formation of the neutral zone. The proposed DPDS route with capsule-free HIP in combination with FEM simulation is demonstrated as a potential route for manufacturing full-density PM steel components, e.g. gears, suitable for high-performance applications.
KeywordsPM steels Gears Pressing Capsule-free HIP Density Finite element simulations
The authors would like to acknowledge Vinnova (Swedish agency for innovation systems) for funding the HIP Gear project (Dnr: 2013-05594) within the framework of the FFI programme. Magnus Ahlfors from Quintus Technologies AB is acknowledged for supporting with the HIP trails.
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