Advanced Materials Research Vol. 445

Abstract: In this study surface finish and dimensional charactersitics of castings produced with gypsum bonded block investment moulds were investigated. Commercial and laboratory made gypsum bonded investment moulds were used for investment casting mould making. To compare the casting quality of the investment powders, wax patterns for surface roughness specimens and linear dimension measurement specimens were designed and produced with special geometry. Wax trees were assembled with these patterns, cylindrical stainless steel perforated flasks were settled around the trees and gypsum bonded investment slurries were filled into flasks. Conventional tin bronze was subsequently cast into these moulds by vacuum assisted casting process. Afterwards, surface roughnesses of specimens were measured and linear dimensions of wax patterns and cast specimens were compared to determine percantage of dimensional change.

Abstract: Sintering is a key step in the metal injection molding (MIM) process, which affects the mechanical properties of the sintered part. The mechanical properties of the sintered compacts are resulted from tremendous sintered part densification. This work utilizes robust engineering technique in optimizing sintering parameters of metal injection molding compacts. Three quality characteristics; shrinkage, density and flexure strength is optimized using Taguchi method-based grey analysis. The modified algorithm adopted here was successfully used for both detraining the optimum setting of the process parameters and for combining multiple quality characteristics into one integrated numerical value called grey relational grade. The sintering parameters investigated are: sintering temperature, sintering time, and heating rate. The result concluded that sintering time is the most significant for the combination of the quality characteristics.

Abstract: In this paper, a transientdynamic analysis is presented for large deformation of powder forming process. The technique is employed using the contact friction algorithm and plasticity behavior of powder. The contact algorithm is applied by imposing the contact constraints and modifying the contact properties of frictional slip through the node-to-surface contact algorithm. A double-surface cap plasticity model is used for highly nonlinear behavior of powder. In order to predict the non-uniform density and stress distributions during powder die-pressing, the numerical schemes are examined for accuracy and efficiency in modeling of a set of powder components.

Abstract: The prediction of flow pattern and volume fraction distribution in ceramic powder injection moulding (CIM) is very important because their characteristics affect the mechanical stiffness and the sintering shrinkage. The definition of feedstock behavior in the simulation of CIM depends on the various parameters such as temperature, strain rate and volume fraction. The aim of this study is to generate the governing equation based on non-newtonian flow model and predict the distribution of volume fraction from the result of CIM simulation using the subroutine of finite element package. Material parameters of governing equation are obtained from the compressive test of feedstock. Initial volume fraction is defined as the value of 0.5 referred to experimental data. In the boundary condition, the velocity of injection is 3 mm/s and the frictional coefficient between the feedstock material and the die is assumed as the value of 0.7 which means the value in the condition of cold moulding. The flow pattern of feedstock is very consistent with the experimental result. The result indicates that the range of volume fraction is from 0.42 to 0.58 depended on the pressure distribution. This result aids to predict the material stiffness according to the location of product from the relationship of the volume fraction and stiffness via Micro-hardness test.

Abstract: This paper presents a new fabrication process for producing magnesium alloy components via metal injection moulding (MIM). Here, four kind of feedstock with 62, 64, 66 and 68% powder loading were prepared by a mixture of gas atomized ZK60 magnesium alloy powder with a resin consisting of palm stearin and low density polyethylene. The rheological investigation of the feedstock was carried out and the optimal powder loading was determined. The optimal powder loading feedstock was then injected by screw type injection moulding machine. The effects of injection moulding parameters on the physical and mechanical properties of green compacts were evaluated. The results showed that injection moulding of a feedstock containing 64% magnesium alloy was possible at high barrel temperature and pressure.

Abstract: Piezoceramics are usually shaped into three dimensional bulk form using dry pressing or slip casting methods. However, certain applications require piezoceramics to be shaped in one dimensional fiber or two dimensional ribbon form. In this study, piezoceramic fibers and curved piezoceramic ribbons were fabricated using a novel alginate gelation method. Alginate is a natural linear polymer that is obtained from brown kelp. In the presence of multivalent cations, it forms ionic cross-links and gels in a three dimensional network form. In our study, gelation conditions of alginate containing aqueous slips of lead zirconate titanate based piezoelectric ceramic powders were investigated. Piezoelectric ceramic fibers and ceramic ribbons were prepared by sintering of gelled powders for transducer applications. Structural characteristics of these ceramics and electrical characteristics of piezodevices prepared from these ceramics were investigated and reported.

Abstract: This paper outlines the findings of an on-going research study investigating the properties of a range of steel and titanium-based micro-lattice structures manufactured using the selective laser melting (SLM) technique. Initially, tension tests have been conducted on strands manufactured at different build angles. Micro-lattice block structures, with struts oriented at +/-45^o were then tested in compression at quasi-static rates of loading. The failure mechanisms have been investigated using both optical and scanning electron microscopy. These tests have highlighted the attractive properties offered by these complex architectures.

Abstract: Flexural motion of a cantilever bar can be used to monitor the taper angle measurements of the bar without incorporating any geometric measurement. This provides non-destructive taper measurement with fast processing in manufacturing line. The laser ablation of a free end of the cantilever bar enables to generate a recoil pressure at the irradiated surface while resulting in external forcing function for the initiation of the flexural motion. Consequently, in the present study, laser induced ablation of free end tapered cantilever bar and resulting displacement and frequency of the flexural motion is examined. The study is extended to include influence of positive and negative bar taper angles on the flexural characteristics. In addition, deviation of displacement and frequency of the flexural motion due to tapered bar from the parallel bar is examined. It is found that the flexural characteristics of the tapered bar enable to determine taper angle of the bar with high accuracy.

Abstract: Laser cutting of ceramics offers considerable advantages over the conventional cutting methods. Some of these advantages include precision of operation, high speed processing and low cost. In addition, cutting process is independent of the mechanical properties of the ceramic material such as hardness and fracture toughness. Alumina is one of the widely used ceramics in industry due to their resistance to harsh environments. Laser cutting of alumina requires high laser power due to high latent heat of melting and elevated melting temperature. In efficient laser cutting process, the low laser power is required. Consequently, for optimum laser cutting conditions of alumina tiles, the thermal efficiency of the cutting process may not be a maximum. The optimum laser cutting parameters provide crack free and parallel edge cuts. Therefore, investigation into laser cutting of alumina ties and the efficiency analysis becomes essential. In the present study, laser cutting of alumina tiles with 3 mm thickness is carried out and thermodynamic analysis associated with the efficiency analysis is introduced. The lump parameter method is incorporated in the thermodynamic analysis. The optimum cutting conditions are then related to the first and second law efficiencies.

Abstract: Tailor Welded Blanks (TWB) are blanks in which two or more sheets of similar or dissimilar materials, thicknesses, coatings etc. are welded together to form a single sheet before forming. Forming behavior of TWBs is affected by thickness ratio, strength ratio, weld conditions such as weld properties, weld orientation, weld location etc. In this work, Nd:YAG laser welding will be use to weld TWB with different thickness in experimental test. Nd:YAG laser welding parameters such as pulse duration, welding velocity, frequency and peak power will affect formability of TWBs. Taguchis design of experiments methodology is followed to design of experiment and obtain the percentage contribution of factors considered. Erichsen formability test and uniaxial tensile test (ASTM-E8) will be use in experiment setup to compare result of different welding parameters on formability quality of TWBs.