Variability of feedstock viscosity and its correlation with dimensional variability of green powder injection moulded components

Abstract

application for PIM, the dimensional precision and variability of the manufactured components need to be further In this study, a correlation between green part dimenunderstood and improved. Recently, substantial part to sional variation and feedstock viscosity variation is part variability has been observed in the green (i.e. injection presented for the powder injection moulding (PIM) moulded) state before the components undergo substantial manufacturing process. A correlation of an increase shrinkage during sintering.4-6 in green part dimensional variation as feedstock vis-The importance of feedstock homogeneity has been cosity variation increases has been found and the pointed out by both part manufacturers and researchers correlation was independent of powder type (316L alike, all agreeing that variations induced in the early gas atomised and water atomised) and mixing process stages cannot be eliminated in the subsequent PIM technique (batch and continuous). The variation of process steps of moulding, debinding and sintering. feedstock viscosity was lowest over the greatest Therefore, the homogeneity of the feedstock can become a temperature range for high shear continuous comcritical characteristic for these later process steps in the pounding with a broad distribution of irregularly PIM process. Inhomogeneities can lead to powder/binder shaped powder. Thus, this feedstock material would separation, defects (e.g. cracks and voids) or increased have the greatest process window for injection moulddistortion and eventually to failure of the PIM manufacturing with the least variation.PM/1049 ing route. Supati et al.7 studied the effects of mixing time, mixing Dr Zauner

Review of Factors that Affect Shrinkage of Molded Part in Injection Molding

“…The grain structure was determined by the binder but can be tuned (from coarse to fine) by mixing suitable waxes: these adds influenced final shrinkage [39]. Dimensional variations were connected to viscosity [41] and affected by processing parameters [40].…”

“…The relationship between polymer morphology and shrinkage involved different aspects of molding processing not always simply to identify. Particle size, powder loading, but especially shear rate and polymer temperature determined the feedstock viscosity [40], and the viscosity was directly related to shrinkage of molded part [41].…”

“…This pressure (lower than the injection pressure) permitted the final filling of the mold by packing the molecules together. Holding pressure was applied until the gate freezes: once that happened, the [41] HDPE þ MW Binder structure [42] 316L feedst. Viscosity [43] 316L feedst.…”

Micro metal injection molding (MicroMIM)

“…A detailed analysis of the influence of the injection 13.3 Tooth brackets made of Ni-free steel alloy (courtesy of Bernhard Fö rster GmbH, Pforzheim, Germany). molding parameters on the precision of the molded parts is given, for example, in (Billiet, 1985;Zauner et al, 2004;Greene and Heaney, 2007;Li et al, 2007;Beck et al, 2008;. Depending on the powder particle sizes and filling rates, the reproducibility of component dimensions is ±0.3 to ±0.5% for metals, ±0.5% for alloyed powders, and ±0.2 to ±0.5% for ceramics.…”

Development of Metal Plate with Internal Structure Utilizing the Metal Injection Molding (MIM) Process

“…For the manufacturing of double-sided metal plates with internal structure, a sacrificed part and polymer insert were necessary [ 10 , 11 ]. The initial design of the structure of the final part was executed as a square type of 30 mm with a total thickness of 2.4 mm, including a polymer insert of 0.8 mm and double-sided metal plates of 0.8 mm each.…”