Papers by Keyword: Green Density

Abstract: For producing higher density PM parts a new method, High-Velocity Compaction process with additional upper relaxation assist (URA) device is presented in the paper. Using zinc stearate as a die wall lubricant, iron powder was pressed with and without upper relaxation assist device of mass 0.14 Kg focusing to investigate the density and mechanical properties. To explain a compaction process in loading stage a conservation of momentum principle has been introduced during collision of hammer, upper piston and upper relaxation assist device in die compaction. To observe the morphological characteristics and mechanical properties, a scanning electron microscopy (SEM) and computer controlled universal testing machine were used. The experimental results showed that the samples compacted with URA device had an improved green density and mechanical properties compared to the samples compacted in the absence of URA device.

Abstract: This study investigates the effects of injection temperature and pressure on green part density. The high density of the green parts for the ceramic injection molding (CIM) process improves the material properties of the final product. In this study, the feedstock used was a combination of alumina and zirconia powders with a binder consisting of high density polyethylene, paraffin wax, and stearic acid. Powder loading was fixed at 57% volume. A standard screw-type injection molding machine was used to produce the green parts. The density of the green parts was measured using the Archimedes method. Experimental results show that a 160 °C injection temperature and a 110 MP_a injection pressure were the optimum parameters to achieve high density of the green parts. In addition, defect-free green parts were obtained.

Abstract: Conventional methods for preparing ceramic bodies, such as cold isostatic pressing, gypsum-mold slip casting, and filter pressing are not completely suitable for fabricating large and thick ceramic plates, because of disadvantages such as the high cost of equipment, formation of density gradient, and differential shrinkage during drying. These problems could be avoided by employing step pressure-vacuum hybrid slip casting in which consolidation occurs not only by the compression of the slip in casting room, but also by vacuum sucking of the dispersion medium (water) around the mold. This method enabled us to fabricate a 110 × 110 × 20 mm alumina plate without cracks and with homogenous density, and the possibility of extending the method to fabricate other ceramic products appears to be promising.

Abstract: Powder metallurgy is a conventional technique for making engineering articles from powders. Main objective is to produce final products with the highest possible uniform density, which depends on the initial loose powder characteristics. Producing, handling, characterizing and compacting materials in loose powder form are part of the manufacturing processes. Density of loose metallic or ceramic powder is an important parameter for die design. Loose powder density is required for calculating the exact mass of powder to fill the die cavity for producing intended green density of the powder compact. To fulfill this requirement of powder metallurgical processing, a loose powder density meter as per ASTM standards is designed and fabricated for measurement of density. The density of free flowing metallic powders can be determined using Hall flow meter funnel and density cup of 25 cm³ volume. Density of metal powders like cobalt, manganese, spherical bronze and pure iron is measured and results are obtained with 99.9% accuracy.

Abstract: High velocity compaction technology was used to press 316L stainless powders. Effects of impact times on stress wave, green density and ejection force were analyzed. It was found that under the same total impact energy, the first loading time and the actuation duration of the second impact in double impact process were longer when compared with single impact process, while the first delay time was shorter. Furthermore, the green density of compacts prepared by double impact was greater than that prepared by single impact, but no obvious variation in maximum ejection force can be observed between single impact and double impact process.

Abstract: In order to develop high density powder metallurgy forming technology, a new concept combining high velocity compaction and warm compaction called warm high velocity compaction (WHVC) was presented. A new warm high velocity compaction forming equipment which adopts gravitational potential energy instead of hydraulic cylinder as hammer driver was designed. By means of the newly developed equipment, a preliminary study on warm high velocity compaction was performed. 316L stainless powder compacts with green density of 7.47 g/cm3 were obtained; the density is much higher than those prepared by conventional high velocity compaction. These results demonstrate that the newly designed equipment can basically meet the demand of warm high velocity compaction and the new forming method is superior to the conventional high velocity compaction. In addition, Densification mechanism of WHVC was also discussed.

Abstract: In this paper, the titanium alloy powder of Ti-6Al-4V is mixed with binder 60wt% of palm stearin and 40wt% of polyethylene for metal injection molding (MIM) process. Injection molding parameters has been optimized using Taguchi method of L27 (313) orthogonal array. Highest green density has been identified as the green part quality characteristic or as an output for this study. Parameters optimized are the injection pressure, injection temperature, powder loading, mold temperature, holding pressure and injection speed. Besides those, interaction of the injection pressure, injection temperature and powder loading were studied. The analysis of variance (ANOVA) is employed to determine the significant levels (α) and contributions of the variables to the green density. Results show that the injection pressure has highest significant percentage followed by injection temperature, powder loading and holding pressure.

Abstract: The high pressure compaction without internal lubricant and the high green density even with the pore free density were achieved by the newly developed die wall lubricant for warm compaction. This developed die wall lubricated warm compaction followed by high temperature sintering resulted in improved mechanical property and almost no dimensional change. In this paper, the effects of increasing the green density on the sintered density, the dimensional change and the mechanical property are mainly discussed.