Papers by Keyword: Dimensional Stability

Abstract: Injection molding is one of the most extensively employed manufacturing methods to produce high quality part at high production rate. However, achieving high precision and quality product is still one of the biggest challenges in injection molding process. In this study, the optimal value of injection molding parameters is investigated. The initial injection parameters are determined using Moldflow software, then it is tested in experimental setup with feedstock composition of 90% Cu and 10% PA-6. After the experiments are done, the optimal combined response can be calculated Taguchi-grey-fuzzy method. Furthermore, ANOVA is done to measure how much contribution is given by each of parameters. From the analysis, it is given that 10 MPa and 9 MPa is the optimal value of both injection pressure and holding pressure respectively. It is also noted that the holding pressure had a higher contribution (39.62%) than injection pressure (13.13%) on the dimensional change and roundness.

Abstract: An experimental study of the physical and mechanical properties of untreated and acetylated wood was conducted. The effect of acetylation on wood density was investigated. It was established that the density of the samples generally decreases after acetylation. As the level of acetylation increases, the fiber saturation point decreases in both conifers and hardwoods. Acetylation of wood helps to reduce the sorption properties of wood. The amount of swelling was analyzed. For untreated wood (aspen and alder), the volume swelling index is at the level of 7.5 %. Acetylation contributes to the stability of the geometric dimensions of structures, as the volume swelling index for aspen decreased by 4 times, for alder – by 2 times. An increase in the amount of swelling along the fibers is observed in all samples. Regarding the nature of the destruction of the samples during compression, the aspen (both untreated and acetylated) only crumples without visible signs of destruction. In some samples of alder, partial exfoliation is visible. It was found that acetylation has an ambiguous effect on the mechanical properties of wood of both species.

Abstract: Aluminium bronze alloys are special copper alloys that have a machinability rate from 20 to 40% compared to free cutting brasses, so the cutting parameters and type of tools suitable for machining of these materials may be very different for other copper alloys. Also, due to the relative high costs of the raw material, the absence of contamination of the chips by cutting fluids improve its intrinsic resales value and encourage the use of machining process without coolant. The aim of this work is to evaluate the tool wear mechanisms in the finishing machining of the Cu-10wt%Al-5wt%Ni-5wt%Fe aluminium-bronze alloy with carbide and cermet inserts at different cutting speeds under dry machining condition. The turning of material showed lower surface roughness in higher speed conditions and better dimensional stability at lower speeds. It was observed the formation of continuous chips, but of little volume occupied. The scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses of tool wear show the adhesion as the main tool wear mechanism, followed by abrasion. At the lower cutting speed, the adhesion wears affected significantly the surface finish, reducing the tool life in comparison to the higher speeds.

Abstract: In this study, Silver birch (Betula pendula) wood veneers and solid wood blocks were treated with commercial phenol-formaldehyde (PF) resin water solutions. Birch veneers and solid wood blocks of different size were impregnated with PF resin solutions in water with concentrations of 10, 20 and 30 wt%. The weight percent gain (WPG) and bulking after drying and curing of resin treated wood specimens were determined to evaluate the impact of specimen sizes and density. The leaching procedure according to EN 84 was performed to evaluate the PF resin fixation stability. The anti-swelling efficiency (ASE) of untreated and treated specimens during seven soaking-drying cycles was examined. Higher WPG values were obtained for specimens with lower density, but no correlation was found between the specimen size and WPG. The WPG of veneers and solid wood was 8.7 - 17.7% and 8.5 - 24.4%, respectively. The ASE of wood blocks treated with PF resins after the 1^st cycle was in the range of 37 - 51% depending on the resin loading in the wood. However, the ASE values decreased after every next soaking-drying cycle, reaching 33 - 48% after the 7^th cycle. After leaching, the WPG of specimens decreased by 2.3 - 3.0%.

Abstract: Quenching residual stresses in Al-Mg-Si alloy forged disc were balanced via cold deformation compression method. In this experiment firstly, the forged disc of Φ210x52 mm was prepared from extruded stock material of Φ160x90 mm through close die forging technique. Next, the forged discs were quenched in water and cold compressed immediately. Finally, the discs were artificial aged to finish in T652 temper. Close die forging and cold compression deformation was performed on a 1200 Ton hydraulic forging press. The amount of cold compression deformation was varied from 2.0 to 5.0% to gauge the optimum level of cold compression for the removal of quenching residual stresses. The residual stresses were measured in terms of dimensional stability of the machined component. Results showed that the 3.8% cold compression deformation was the optimized value for the work piece geometry under investigation. Further, the effect of cold (room temperature) and hot water (~60°C) quenching on the residual stresses was also studied and compared with that of cold compression method.

Abstract: AISI D2 tool steel has become important material in the industry, especially for mold and dies maker and also used for cutting tools. Conventional hardening process such as annealing and quenching is normally done for this kind of steel as it needs high hardness and wear resistance properties. To further improve its performance, sub-zero treatment can be performed. Quenching the steel in very low temperature e.g. liquid nitrogen, will help to remove unwanted retained austenite, thus provide better dimensional stability. In this study, AISI D2 tool steel samples were subjected to austenitizing temperature of 1030°C and then quenched using different quenching media i.e. air, oil, and liquid nitrogen. Vickers test result showed that after quenching process, the hardness for those samples were 762 HV, 822 HV, and 735 HV for air, oil, and liquid nitrogen quenched respectively. Microstructure analysis showed that retained austenite volume fraction after quenching process were 7.50%, 3.93%, and 3.18% for air, oil, and liquid nitrogen quenched respectively.

Abstract: In this paper we studied the behavior of some impression materials such as alginate, condensation and addition silicones, considering the following parameters: the reproductive capacity of morphological details - dimensional stability - the ability to reproduce with accuracy the ratio between morphological elements. The essential conditions that an impression material should fulfill are plasticity, fidelity, flexibility, good mechanical strength, dimensional stability, suitable setting time and compatibility with materials from which the models are manufactured.The study results indicated that condensation silicones present the highest volumetric changes, their contraction being the result of the evaporation of volatile byproducts.The dimensional stability of fingerprint materials is one of the variables that contribute to the accuracy or inaccuracy of dental prostheses, other factors being represented by the changes occurring during the preparation of the fingerprint material as well as the fingerprinting techniques.

Abstract: Material with ultra-low coefficient of thermal expansion (CTE) is required for mounting camera and other optical elements in satellite systems. Invar (64 Fe 36Ni) has been the work-horse material for this purpose. In recent years, modified version of conventional invar i.e. Superinvar with 5% cobalt (replacing 5% nickel) is being used to further bring down the errors in camera mountings due to thermal expansion. Processing of this alloy poses many challenges due to its requirement of ultra-low CTE. In the present work, melting and thermomechanical processing parameters were selected to meet the specified requirement of the alloy. The alloy was melted through vacuum induction melting process to obtain uniform and homogeneous chemistry and properties. Virgin raw material was used to achieve lowest carbon and manganese contents. Chemical composition thus obtained is found to be within the specification. Material was hot worked to refine the microstructure. Three different sizes of forged blocks were produced. Hot worked material was heat treated to obtain desirable and stable microstructure. Heat treatment cycle for stabilization was selected and used to retain carbon in the solution and minimize temporal growth. Mechanical properties (tensile strength and modulus of elasticity) and physical properties (CTE, thermal conductivity) were evaluated. Properties were found to be meeting the specification. It is observed that the material shows uniform single phase austenitic microstructure. The paper presents details of the process selection and challenges in processing of this alloy to obtain the targeted CTE < 0.6x10^-6 per °C in the temperature range of 25°C to 150°C along with other desired mechanical properties.

Abstract: Sulfonated poly (arylene ether sulfone) s (SPAESs) exhibit good proton conductivity, thermal and mechanical properties, could act as candidates of proton exchange membranes for fuel cells. At the same time, the poor oxidative stability and excessive swelling ratio of SPAESs bring limitations for its further use. In this article, PAN was employed to mix with SPAES, and then SPAES/PAN blend membranes were prepared from the blend solution by casting. The water uptake, dimensional and oxidative stability, proton conductivity were measured with respect to the addition content of PAN, the phase morphology of the resultant SPAES/PAN were also observed by SEM. The results explained that the corporation of PAN into SPAES could reduce the water uptake and improve the oxidative stability of the obtained membranes compared with the pristine SPAES membrane. That the PAN phase distributed as separated domains in SPAES matrix was found, the interaction between SPAES and PAN may be present, which is responsible for the improvement of dimensional and oxidative stability. Although the proton conductivity of the blend membranes became reduced with increase of PAN content in the SPAES/PAN blend, the conductivity of 0.0265S/cm at 30°C could still be reached, satisfying the requirement for proton exchange membrane Fuel Cell

Abstract: O-MMT treated unsaturated polyester based hybrid composites were prepared using keratin fiber obtained from chicken feathers. Fibers of similar dimension were selected to fabricate composites through hand lay-up method. The preparation and dimensional stability properties of keratin fiber as reinforcements in composites is outlined in this paper. Varying O-MMT contents in nancomposites is performed to investigate the effects on the dimensional stability (water absorption and thickness swelling) of the composites. Results indicated that increasing fiber content deteriorates dimensional stability of the composites and composites. However, improvements in dimensional stability of the keratin fibercomposites were observed with O-MMT. O-MMT treatment reduces the water absorption and thickness swelling, especially at 5wt% of O-MMT concentrationat all range of fiber content. At 5wt% concentration of O-MMt, 10wt% keratin fiber content marks the lowest water absorption and thickness swelling with rate of 0.65% and 1.93%, respectively. Adopting 10wt% of keratin fiber at 5wt% of O-MMT can be utilized for application requiring high dimensional stability.