Research Progress on Low-Pressure Powder Injection Molding

Powder injection molding (PIM) is a well-known technique to manufacture net-shaped, complicated, macro or micro parts employing a wide range of materials and alloys. Depending on the pressure applied to inject the feedstock, this process can be separated into low-pressure (LPIM) and high-pressure (HPIM) injection molding. Although the LPIM and HPIM processes are theoretically similar, all steps have substantial differences, particularly feedstock preparation, injection, and debinding. After decades of focusing on HPIM, low-viscosity feedstocks with improved flowability have recently been produced utilizing low-molecular-weight polymers for LPIM. It has been proven that LPIM can be used for making parts in low quantities or mass production. Compared to HPIM, which could only be used for the mass production of metallic and ceramic components, LPIM can give an outstanding opportunity to cover applications in low or large batch production rates. Due to the use of low-cost equipment, LPIM also provides several economic benefits. However, establishing an optimal binder system for all powders that should be injected at extremely low pressures (below 1 MPa) is challenging. Therefore, various defects may occur throughout the mixing, injection, debinding, and sintering stages. Since all steps in the process are interrelated, it is important to have a general picture of the whole process which needs a scientific overview. This paper reviews the potential of LPIM and the characteristics of all steps. A complete academic and research background survey on the applications, challenges, and prospects has been indicated. It can be concluded that although many challenges of LPIM have been solved, it could be a proper solution to use this process and materials in developing new applications for technologies such as additive manufacturing and processing of sensitive alloys.

An Overview of Highly Porous Titanium Processed via Metal Injection Molding in Combination with the Space Holder Method

In the past two decades, titanium foams have attracted greater interest from the biomedical industry due to their excellent chemical and mechanical biocompatibility when used as biomimetic implants. The porous structure plays an important role in bone adhesion to an implant, allowing its growth into the component. Moreover, the voids reduce the elastic modulus, promoting greater compatibility with the bone, avoiding the stress shielding effect. In this regard, metal injection molding is an attractive process for titanium foams manufacturing due to the high microstructural control and the possibility of producing, on a large scale, parts with complex near-net-shaped structures. In this review, recent discoveries and advantages regarding the processing of titanium powders and alloys via metal injection molding combined with the space holder method are presented. This approach can be used to obtain foams with high biocompatibility with the human body at a microstructural, chemical, and mechanical level.

Exploration of gum ghatti-modified porous scaffolds for bone tissue engineering applications

Taking advantage of the tissue engineering principles, the formed hydroxyl apatite-modified gum ghatti biomaterial with its porous nature, biocompatibility, and efficient mechanical properties can be potential for the bone repair and regeneration.

A comprehensive review of recent developments in 3D printing technique for ceramic membrane fabrication for water purification

Additive manufacturing (AM), which is also commonly known as 3D printing, provides flexibility in the manufacturing of complex geometric parts at competitive prices and within a low production time. However, AM has not been used to a large extent in filtration and water treatment processes. AM results in the creation of millions of nanofibers that are sublayered on top of each other and compressed into a thin membrane. AM is a novel technique for fabricating filtration membranes with different shapes, sizes and controlled porosity, which cannot be achieved using conventional process such as electrospinning and knife casting. In this paper, we review the advantages and limitations of AM processes for fabricating ceramic membranes. Moreover, a brief background of AM processes is provided, and their future prospects are examined. Due to their potential benefits for fabrication and flexibility with different materials, AM methods are promising in the field of membrane engineering.

Additive manufacturing (AM), which is also commonly known as 3D printing, provides flexibility in the manufacturing of complex geometric parts at competitive prices and within a low production time.

Effect of sintering parameters on physical and mechanical properties of powder injection moulded stainless steel-hydroxyapatite composite

The combination of metallic bio-inert material, stainless-steel 316L (SS316L) and a bio-active material, hydroxyapatite (HA) can produce a composite which has superior properties for orthopaedic applications. The main objective of this study is to investigate the effects of sintering temperature and holding time on the physical and mechanical properties of the sintered part. 50wt.% SS316L and 50wt.% HA were mixed with a binder system of palm stearin (PS) and polyethylene (PE) at 61 vol.% powder loading. Rheological properties show a pseudo-plastic behaviour of the feedstock, where viscosity decreases with increasing shear rate. The feedstock was injection moulded into a tensile bar shape while thermal debinding was carried out at 320°C and 500°C. The brown parts were sintered at 1000, 1100, 1200 and 1300°C, with three different sintering times of 1, 3 and 5 hours in the furnace. It was found that the highest sintered density measured was 95.61% of the theoretical density. In addition, the highest hardness and Young's modulus measured were 150.45 HV and 52.61 GPa respectively, which are higher than those of human bone. The lowest percentage of carbon content was 0.022wt.% given by the sample sintered at 1300°C for 1 hour. Therefore, SS316L/HA composite with good mechanical and physical properties was successfully produced through the PIM process.

Microstructure evolution and enhanced bioactivity of Ti–Nb–Zr alloy by bioactive hydroxyapatite fabricated via spark plasma sintering

The crystalline phases and bioactivity of materials play crucial factors in determining the biological interactions and osseointegration process of orthopaedic replacements or implants.

A Study of Polyvinyl Butyryl Based Binder System in Titanium Based Metal Injection Moulding

Metal injection moulding (MIM) is an innovative injection moulding technique widely used to produce complex shaped components from feedstock composed of metal powders and thermosetting or thermoplastic binders. In MIM, binder selection and formulation are considered as critical processes since binder characteristics dictate the success of MIM. The purpose of this study is to determine the feasibility of polyvinyl butyryl (PVB) based binder system in Ti-6Al-4V(wt.%)/binder feedstock, as well as to understand the effects of key parameters, such as powder loading and mixing conditions on the rheological properties of a feedstock. In this study, PVB, polyethylene glycol (PEG), and stearic acid (SA) were chosen to formulate a multi-component binder system to prepare Ti-6Al-4V based feedstock with the aid of three types of mixers: a compounder, a modified mechanical mixer and a twin screw extruder. Further, morphological analysis was performed using optical microscopy and scanning electron microscopy. Thermal analysis was performed using simultaneous differential thermal analysis and thermogravimetric analysis. Results showed that binder formulation was reasonably successful with the aid of both mechanical mixer and a twin screw extruder under certain mixing conditions, and the critical powder loading was 68 vol.%, resulting in an optimum powder loading of 63 vol.% .