Effect Of The Interaction Between Stainless Steel Powder And Binder On Metal Injection Moulding

Metal injection moulding?MIM?is a net-shape forming processing for producing complex shaped parts quickly.The compatibility of binder and powder directly affects the characteristic of feedstock.In general,good compatibility means good wettability and good adhesion.In this paper,the powder surface was modified and the binder was functionalized.Powder and binder were connected by hydrogen bonds or chemical bonds,and the increased interaction made green parts high density,high mechanical strength and good shape retention in debinding.The specific contents are as follows:KH550 coupling agent was used to modified the surface of 17-4PH stainless steel powder,in order to graft amino group to the surface of powder.Then characterizations of powder before and after modification were tested by sedimentation volume,surface elements and particle size distribution.Methyl methacrylate?MMA?was copolymerized with hydroxyethyl methacrylate?HEMA?and glycidyl methacrylate?GMA?,respectively.The functional copolymer was component of binder.By changing the molar ratio of the monomers,a series of P?MMA-co-HEMA?copolymers?PMH?with hydroxyl groups and a series of P?MMA-co-GMA?copolymers?PMG?with epoxy groups were synthesized.The binder consisted of 70 vol.%functionalized copolymer and 30 vol.%polyethylene glycol?PEG1500?.The effects of the interaction force between stainless steel powder and binder on the fluidity of feedstock,green part density,strength and debinding process were investigated.The results showed that as the interaction between powder and binder increased,the density and strength of green part were significantly improved.The melt index of feedstock reached in range of 42-65 g/10min?230°C,2.16 kg?,which could meet the requirements for melt flowability of injection moulding.In addition,the density increase of green part was increased about 0.08 g·cm^-3,and the strength of green part was improved,its compression modulus reached 1330 MPa.The debinding process was optimized.The effects of interaction,debinding method, time,atmosphere and green part size on the debinding rate and shape retention were explored.The experiment found that green part composed of modified powder and PMG binder had better shape retention and dimensional stability.Compared with the direct thermal debinding,using two-step debinding method?water extraction and thermal debinding?the green part did not have the defects of expansion,cracking and holes,and the macroscopic appearance and microstructure of the sample remained intact.