Bi-phasic Simulation of Metal Injection Moulding:Constitutive Determinations

To predict the segregation effect in metal injection moulding (MIM) injection, a bi-phasic model based on mixture theory is adopted in simulation. An explicit algorithm is developed and realized by the authors, which conducts the simulation to be a cost-effective tool in MIM technology. In case of the bi-phasic simulation, the viscosity behaviours are necessary to be determined for the flows of each phase while only the viscosity of mixture is measurable by tests. It is a crucial problem for application of the bi-phasic simulation of MIM injection. A reasonable method is hence analysed and proposed to determine the viscosity behaviours of each phase. Even though this method may be furthermore modified in the future, it results in the practical simulation of segregation effects with reasonable parameters. The simulation results are compared with the measurements on injected specimens.

Extrusion Based Additive Manufacturing of Metal Parts

AM （additive manufacturing） of metal parts becomes increasingly important in many industrial fields. However, currently used AM processes like laser melting or electron beam melting are quite complex and expensive. The extrusion based AM technology for dense metal components （Composite Extrusion Modelling-CEM）, is characterised by an easy handling and cost efficiency in comparison to powder based processes. The CEM process contains two steps, the additive manufacturing of the green parts and the consecutive sintering. The additive manufacturing of green parts is carried out in a thermally controlled extrusion process. The standard metal injection moulding material with a high proportion of metal and thermoplastic binder is deposited in layers by a heated nozzle. In this way overhangs and bridge structures can be realised. The quality of the green parts that were manufactured with the specifically developed extruder corresponds to typical Fused Deposition Modelling parts. In case the surfaces need to be smooth the green parts can be mechanically post-processed before going through the debinding and sintering process.

A New Explicit Algorithm for Bi-Phasic Mixture Flow in MIM

Metal injection moulding (MIM) is a new technology to manufacture small intricate parts in large quantity. Numerical simulation plays an important role in its development. To predict the specific segregation effect in MIM injection, mixture theory is adopted to model the injection flow by a bi-phasic model. This model conducts to the solution of two-coupled Stokes equations. It is an extremely computational consuming solution in the scope of the traditional algorithms, which induce a serious challenge to cost-effectivity of the MIM simulation. Referred to some methods proposed by Lewis in mono-phasic simulation and the implicit algorithms in MIM simulation, a new explicit algorithm is proposed and realized to perform efficiently this type of bi-phasic flow. Numerically this algorithm is devised to perform the simulation in a fully uncoupled manner except for a global solution of the pressure field in each time step. The physical coupling is taken into account in a sequential pattern by fractional steps.

Using fused filament fabrication to improve the tribocorrosion behaviour of 17-4 PH SS in comparison to other metal forming techniques

Fused filament fabrication(FFF)is one of the additive manufacturing processes which has gained more interest because of its simplicity and low-cost.This technology is similar to the conventional metal injection moulding(MIM)process,consisting of the feedstock preparation of metal powder and polymer binders,followed by layer-by-layer 3D printing(FFF)or injection(MIM)to create green parts and,finally,debinding and sintering.Moreover,both technologies provide near-dense parts.This work presents an in-depth study of the processing method’s influence.The porosity,microstructure,hardness,corrosion,and tribocorrosion behaviour are compared for 17-4 PH SS samples processed from powder by additive manufacturing using FFF and MIM,as well as conventional powder metallurgy(PM)samples.MIM samples exhibited the highest macro and microhardness,while corrosion behaviour was similar for both MIM and FFF samples,but superior in comparison to conventional PM samples.However,the FFF-as fabricated samples displayed a significant improvement in tribocorrosion resistance that could be explained by the higher proportion of delta ferrite and retained austenite in their microstructure.

Biocompatibility of MIM 316L stainless steel

To evaluate the bioeompatibility of MIM 316L stainless steel,the percentage of S-period cells were detected by flow cytometry after L929 incubated with extraction of MIM 316L stainless steel,using titanium implant materials of clinical application as the contrast.Both materials were implanted in animal and the histopathological evaluations were carried out.The statistical analyses show that there are no significant differences between two groups(P>0.05),which demonstrates that MIM 316L stainless steel has a good biocompatibility.

Microstructure and mechanical properties of complex-shaped 7075 aluminium alloy prepared using modified polyoxymethylene-based feedstock

Additives of dioctyl phthalate(DOP),ethylene bis-stearomide(EBS),and epoxy(EP)were selected to modify the surface of 7075 Al alloy powder.Functional groups in DOP and EBS form hydrogen bonds with hydroxyl groups on the surface of Al powder.Additionally,the epoxy groups in the epoxy resin undergo ring-opening reactions with hydroxyl groups.The above interactions increased the compatibility between alloy powder and polyoxymethylene(POM).After sintering,samples containing DOP and EP presented high contents of C and O,while the part with EBS additive exhibited the lowest contents of 0.006 wt.%C and 0.604 wt.%O,respectively.Excessive C tends to accumulate at grain boundaries during sintering.Concurrently,excessive O causes secondary oxidation of aluminium alloy powder,inhibiting the sintering densification process.Therefore,the densities of the samples containing DOP and EP were only 85.52%and 79.01%,respectively.In contrast,using EBS as an additive,high-quality aluminium alloy parts were achieved,with a relative density of 97.64%and a tensile strength of 193 MPa.