Eff ect of Injection Moulding Sequences on Mechanical Properties of Two-material Metal Injection Moulding

Abstract

Two-Material Metal Injection Moulding (2M-MIM) process was developed for a component that requires different properties of materials. The materials used in this study were SCM 415, Fe-2Ni and 316L stainless steel (316L SS). The tensile test specimens were injected into 2M-MIM of SCM 415-Fe-2Ni and SCM 415-316L SS. In addition, each alloy was fabricated by MIM as reference samples. The 2M-MIM processes were injected with two different injection moulding sequences, which are “sequential injection” and “simultaneous injection”. The injection process of “sequential injection” specimens is to fi ll a half of the mould with the fi rst alloy and then inject the second half of the mould with the second alloy. The “simultaneous injection” specimens utilised the co-nozzle and co-injected both alloys simultaneously from each end of tensile specimen. The weld line positions of both injection moulding sequences were controlled in the middle at the gauge length. After injection, all specimens were sintered at 1325°C for 2 hrs. The shrinkage of each single-material specimen is 12.20 ± 0.64%, 14.90 ± 1.95% and 13.84 ± 0.24% for SCM 415, Fe-2Ni and 316L SS respectively. The ultimate tensile strength of SCM 415, Fe-2Ni and 316L SS are 549.62 ± 7.87 MPa, 474.08 ± 8.1 MPa and 351.44 ± 0.42 MPa respectively and the elongation is 9.68 ± 0.71%, 23.05 ± 2.64% and 51.33 ± 3.76% respectively. For 2M-MIM, the mechanical properties of the “sequential injection” specimens are more superior than the “simultaneous injection” specimens. This is due to the difference of weld line interface of 2M-MIM. The interface of sample was investigated by SEM and OM. Cracks were observed at the weld line of SCM – Fe-2Ni using “simultaneous injection” and the sharp crack was observed near the edge of specimen all specimens. The ultimate tensile strength of SCM 415-Fe-2Ni specimens and SCM 415-316L SS specimens are 374.42 ± 13.80 MPa and 403.35 ± 31 MPa respectively for “sequential injection” and 223.87 ± 31.98 MPa and 193.75 ± 15.41 MPa respectively for “simultaneous injection”. EDS results across the weld line of SCM 415-Fe-2Ni “sequential injection” specimen show that nickel diffused from Fe-2Ni to SCM 415 while chromium diffused from SCM 415 to Fe-2Ni.