Arif Rochman

Effect of Build Orientation of Electron Beam Melting on Microstructure and Mechanical Properties of Ti-6Al-4V

Build orientation influences thermal activity during the EBM process, thus affecting the resultant bulk material properties of the part being produced. This work focuses on EBM build orientation with respect to the X, Y and Z axes and its effect on microstructure and mechanical performance of Ti-6Al-4V parts. A series of EBM Ti-6Al-4V specimens were fabricated using an Arcam S12 setup in different build orientations: XY, ZX, ZY, XY 30° and XY 60° inclination to the start plate. Using conventionally wrought Ti-6Al-4V as a benchmark, EBM specimens were tensile and impact tested. Furthermore, microhardness measurements, optical and electron microscopy were used for characterization. Horizontally oriented EBM Ti-6Al-4V parts develop finer lamellar microstructures as a result of higher cooling rates, however exhibiting comparable strength and rather lower ductility and toughness when compared to vertically oriented parts. Solidification defects, resulting from inconsistencies in melting due to high cooling rates but also related to specimen geometry, have countered the influence of a finer microstructure. This study has also shown that EBM parts develop columnar prior-β grains which follow build direction. Benchmark wrought Ti-6Al-4V specimens show higher tensile properties while offering increased resistance to crack nucleation due to their homogeneous equiaxed microstructure.

A Process for Semi-Solid Moulding of High Viscosity Thermoplastic Polymers.

A new moulding process for manufacturing micro parts made from high viscosity polymers has been developed as a result of a feasibility study. The process basically involves compression moulding of a polymeric preform by heating it up to its semi‐solid state, i.e. between its glass transition temperature and melting temperature. The apparatus is made up of three main parts: a forming device, a single cavity micro mould and an induction heating system. The processing technique was successfully tested in the manufacturing of 10 mm round discs with a flange and inner bore using high viscosity polymers such as polyphenylene sulfide (PPS), polyetheretherketone (PEEK), ultra‐high molecular weight polyethylene (UHMW PE) and polytetrafluoroethylene (PTFE). In a further miniaturization study, U‐shaped micro seals with an outer diameter up to 2.5 mm were also successfully manufactured from non‐injection mouldable PTFE. Thus, the new process is a realistic alternative technique to the existing micro moulding processe...

Influence of melt mixer on injection molding of thermoset elastomers

One of the drawbacks in injection molding is that the plasticizing screw is short such that polymers having high concentrations of additives, such as thermoset elastomers, might not mix homogeneously within the short period of time during the plasticizing stage. In this study, various melt mixers inside the nozzle chamber, together forming a mixing nozzle, were developed. Three different materials were investigated, namely nitrile butadiene rubber (NBR), ethylene propylene-diene monomer (EPDM) and fluorocarbon (FKM). The use of these melt mixers resulted in better homogeneity and properties of the molded parts despite a curing time reduction of 10 s. This was due to the increase in mixing and shearing introduced a higher rate of crosslinking formation in the molded parts.

Design of an Endoscopic Micro Optical Part for Fabrication With Micro Two Shot Injection Moulding

Micro two shot injection moulding (μtwo shot IM) is a manufacturing process capable of simultaneously replicating two polymeric parts and assembling them; removing the requirement for costly micro assembly. Endoscopes are used in medical environments to observe areas that are otherwise unobservable. μTwo shot IM has the potential to simultaneously replicate and assemble polymer lenses for endoscope imaging and assembling them to their required housing. In view of this, this paper contributes a case study part for application of μtwo shot injection moulding in the fabrication of an endoscopic micro optical component. This paper covers several aspects involved in the design of such a part. This novel design concept consists of an optical component and a housing component moulded sequentially on top of each other using μtwo shot IM. The lens component consisted of three lenses with a common base moulded as the first shot. The second shot moulded on onto the optical component was the housing component incorporating an external thread for interchangeability. From a material selection exercise it was concluded that cyclic olefin copolymer (COC) shall be used as the optical material and polyoxymethylene (POM) shall be used as the housing material. One major concern in the design of such a part is the deformation of the optical material by the housing material due to softening via heat transfer. Simulations of such a scenario were carried out and it was indicated that the functionality of the optical material shall not be compromised.Copyright