Sri Yulis M. Amin

Rheological properties of cemented tungsten carbide feedstock for micro powder injection

The rheological behavior of feedstock needs to be examined for manufacturing parts without defects by micro powder injection molding (μPIM). In this study, submicron tungsten carbide (WC) and cobalt (Co) were milled for several hours. The distribution and morphology of the powder mixture were analyzed by laser diffraction and scanning electron microscopy. After measurement of critical powder loading, cemented tungsten carbide (WCCo) powder was mixed with a thermoplastic/paraffin wax binder with a powder loading volume from 50% to 52% to obtain feedstock. The flow properties of the WCCo feedstock were evaluated using a capillary rheometer at different temperatures. It was found that feedstock exhibit a pseudoplastic flow behavior, which is one of the main requirements for μPIM. Feedstock is also shown to be highly sensitive to temperature at high powder loading. Low powder loading led to low viscosity at a high shear rate that cannot be used in μPIM because it results in powder and binder separation.

Ball Milling of WC-Co Powder as Injection Molding Feedstock

In this paper, an attempt has been made to mill constituent of WC and Co powder towards achieving volumetric percentage of WC (91%) and Co (9%). The ball milling technique was conducted under dry and wet condition using various milling parameters, rotation speed, time and ethanol as milling medium. Electron dispersive spectrometer (EDS) detected the elemental distribution, whilst SEM and particle size analysis was done to study the effect of changes in particle morphology and reduction of particle size. As a conclusion, powder milled by parameter of wet milling by ethanol, speed of rotation at 250 rpm and 90 minutes of milling time exhibits best results in term of volumetric percentage of 91%WC and 9%Co and particle size reduction.

Rheological Properties Analysis of WC-Co Injection Feedstock

In order to produce a defect-free component, the feedstock composition plays as a critical factor. The feedstock needs to meet the following criteria; high solid loading with excellent flowability. The flowability of the feedstock is greatly determined by the rheological response. Therefore, the aim of this paper is to investigate the rheological behaviour of MIM feedstock comprising of WC-Co powder, with a binder system of Palm Stearin (PS) and Polyethylene (PE), by means of a capillary rheometry. The viscosity and shear rate of various feedstocks at powder loading ranging from 59, 61 and 63% were measured at L/D = 10 die. The rheological properties such as flow behaviour index, activation energy and moldability parameter of each feedstock were calculated and from the analysis, it was concluded that they show a good pseudo-plastic behaviour within acceptable ranges in MIM.