Key Engineering Materials Vols. 447-448

Abstract: The dynamic recrystallization (DRX) behavior in the isothermal hot compression of AISI 52100 steel was analyzed by using the phenomenological-based cellular automaton (CA) algorithm. The developed CA model was coded into DEFORM platform, which is a Finite Element Method (FEM)-based software for simulation of material deformation process. The developed CA-model can thus predict the nucleation and growth kinetics of dynamically recrystallized grains of the testing material in hot working process. Furthermore, the effects of the deformation temperature, true strain and strain rate on the microstructural evolution of the testing material were physically studied by using Gleeble-1500 thermo-mechanical simulator and the developed CA-model was verified by the experimental results. Through simulation and experiment, it is found that the results predicted by the CA-model have a good agreement with the experimental ones.

Abstract: Powder injection molding technology is currently applied to the joining processes to produce multi-functional components. In this paper, the strength of the joint of green and sintered samples produced by powder injection molding was evaluated using four-point bending test. The microstructures of the green samples showed that a very good joint was formed by the re-melting of the first injection molded half part followed by a high pressure compacting in the second injection molding. The strength of joined green samples was almost equal to the reference green samples without joining. The microstructures and flexure strength of sintered joined samples, which was more than 90% of base materials, showed that the good joining was maintained after sintering. This high strength sintered joint was an integrative result of powder injection molding and sintering diffusion. The crack observed at the sample surface accounted for the slight drop of the strength.

Abstract: This paper is concerned with the deformation and the redistribution process of particles in SnO2/Ag particulate reinforced metal-matrix composites during micro-extrusion. The effects of the extrusion angle, the extrusion ratio and the ram speed on the deformation and redistribution of particles during the forming process were studied by finite element methods using Deform software. The deformation behavior and redistribution pattern are explained based on the non-uniform flow of the billet and the non-uniform stress distribution.

Abstract: There are growing demands from the precision engineering industries for components that are net or near net shape while striving to reduce material wastage during the manufacturing process. This study investigates the spin formability of liquid forged Al-6061 pre-forms into near net shape cylindrical components with high aspect ratios. The liquid forging process offers very significant materials savings by providing pre-forms for the spin forming process. The end products are near net shape components with very good mechanical properties. Results from this study indicate that liquid forging is able to supply Al-6061 pre-forms, otherwise machined from solid bars, which are sufficiently formable for spin forming. The microstructure of a spin formed liquid forged pre-form is also indiscernible from that of a fully machined pre-form from extruded bar stock. As such, spin forming of liquid forged pre-forms has the potential to reduce material wastage and hence production costs.

Abstract: The effect of forming temperature and feed rate on the flaring of AZ31 magnesium cups was investigated in the warm flow-forming process. Flaring is a common phenomenon in flow-forming process whereby the diameter of the work-piece is observed to increase gradually along the flow-formed path. In this study, forward flow-forming process was performed on a cup-shaped work-piece by using two diametrically opposite rollers (approach angle of 20) at a constant thickness reduction. To study the effects on flaring, experiments were performed at feed rates of 0.2mm/rev, 0.4mm/rev, and 0.8mm/rev and at forming temperatures between 50~300°C. Experimental results indicated that feed rate was the most significant parameter influencing flaring while temperature mainly improve the formability of the material. It is believed that a higher feed rate resulted in an increase in metal flow in the circumferential direction because of higher mean circumferential strain and hence increases flaring. Flaring was also observed to be most severe at forming temperature of 300°C and feed rate of 0.8 mm/rev due to the excessive metal flow in the cirucmferential direction of the test-piece. This study clarifies the relationship between feed rate and the extend of flaring and that forming temperature has little influence on flaring from temperature range of 50°C to 250°C.

Abstract: A progressive forming process for micro-components was developed to circumvent the issue of handling of small micro-parts while keeping in mind the need for high manufacturing through-put. The mechanical properties and microstructure of the material have been found to play a significant role in the forming of micro-components. In this work, the effect of mechanical property on the forming of copper micro-pins by the progressive forming process is highlighted. Empirical results show that the forming load decreases for forming micro-pin with 0.3mm diameter after annealing but the pin height obtainable decreases as well compared to that prior to the heat treatment.

Abstract: Conventional superplastic forming has been applied in automotive and aerospace industries for a few decades. Recently, superplastic forming combined with mechanical pre-forming process has been reported to be capable of forming non-superplastic AA5083 at 400 °C to a surface expansion of 200 % [1]. In this paper, finite element modeling (FEM) was used to develop the combined forming process by using the non-superplastic material AA5083-O. The simulation follows the experimental sequence and was divided into two phases (mechanical pre-forming and superplastic forming). A conventional creep equation based on tensile test data was adopted as a material model for the simulation. The pressure cycle and forming time was simulated according to the actual process route. The thickness distributions obtained from simulation validated the capability of the model to be used for this case. The influence of different parameters, such as holder force, friction, and punch depth was investigated by comparing the final sheet thickness and level of material draw-in. It was found that the punch depth played a significant effect on the uniformity of thickness distribution, from which a more uniform formed part can be obtained by using the punch with higher depth during mechanical pre-forming phase.

Abstract: Three-dimensional CAD systems contribute considerably to the detailed design processes of products. They are applied to the construction of 3D design models which are also utilized for design evaluation using a CAE system and for NC data generation using a CAM system. Since the functions of 3D CAD systems for constructing 3D models are increasingly being enhanced, they enable designers to easily construct 3D product models without design expertise. In detailed design work, designers are required not only to exactly define product shapes but also to assign attribute information such as dimensional tolerance, geometrical tolerance, roughness, machining process to be performed etc., which are essential for the manufacturing process. However, inexperienced designers often find it extremely hard to determine optimum attribute values and design values. In addition, it is more difficult to construct the required die/mold from the desired product shape taking into account forming errors caused by shrinkage during plastic injection and springback during press forming. This paper proposes a method to automatically assign required attribute information to each part of a designed product, to assist the model construction of a die/mold from a product shape, and to provide design support information on each part of a designed product to a designer. The proposed method is realized by assigning a Function Feature to each part; all the function features proposed in this paper are original. A CAD system based on the proposed method for injection molding and press forming was developed, and results of simple design experiments confirmed the usefulness of the CAD system and function features

Abstract: In this paper, we have described automatic gathering with visual feedback of egg-cells by 2 miniature robots. Generating a transgenic mouse is one of the most important operations in the bio-medical field. Sometimes scientists need several hundreds of egg-cells for only 1 experiment. However, conventional manipulators are designed for only DNA-injecting, and they are not useful devices for gathering egg-cells. To support the DNA-injecting operation, we have proposed the automatic gathering of egg-cells by 2 miniature robots and a miniature pump. In several experiments, we have checked the efficiency and confirmed that our device has good feasibility to support egg-cell processing. We have also proposed a 5 pipettes’ egg-cell processing method using miniature robots to realize multi-functional and flexible egg-cell processing.

Abstract: We present a process to fabricate Ni moulds on proton beam written (PBW) PMMA structures. These Ni mould are use to replicate PDMS lab on a chip devices featuring 300 nm details of high verticality, smooth sidewalls and high aspect ratios. The lifespan of the Ni mould can be extended and the functionality improved by means of introducing a 5 nm thick Teflon AF release layer. Following this method, PDMS chips have been fabricated for microfluidic experiments.