Papers by Keyword: Micro Metal Forming

Abstract: This study investigated the effects of the die clearance on the shearing and shaving processes of the stainless steel (SUS316LVM) wire at micro scale. A die set was developed and installed on a precession press equipped with a load cell and a displacement sensor to conduct experiments. By using different punches in the same die set, the specimens prepared from 316LVM stainless steel wires with 0.5 mm diameter were first sheared and then shaved. Experimental results show that the burnished area of the sheared edge increases with the reduction of the clearance between the punch and die in the shearing process. The clearance also significantly affects the load curves. Moreover, the shaving process does increase the burnished area on the shaved edge of the specimen. By an appropriate feed in the shaving process, it is possible to trim the extra material from the sheared edge that results in a nearly complete burnished surface on the shaved edge of the stainless steel wire. This research provides a basis for understanding of the die clearance effect on the shearing and shaving processes at micro scale.

Abstract: This study used finite element simulations and experiments to investigate the forming limit in the nosing process of micro copper cups, and to establish the limit nosing curves in terms of nosing ratio, die angle, and friction factor. Two-stage processes, including backward extrusion and nosing processes, were considered in simulations and experiments at micro scale. The copper billets with 1 mm diameter and length were backwards extruded to produce the 1 mm diameter cups with 0.1 mm wall thickness. The cups were later used in the nosing processes under different forming conditions. By analysing the results of the nosed cups from the simulations, it is possible to identify the safe and failure forming conditions and establish the limit nosing curves for the nosing process. The simulation results show that the limit nosing ratio increases as the die angle or friction factor decreases. Two predicted results for poor and well lubricated conditions have been examined and are in good agreement with those from experiments. The study not only explores the characteristics of the noise process of copper cups at micro scale but also establishes the limit nosing curves which could be the guidelines for the design of micro metal components.

Abstract: The study investigated the effect of grain size on the micro deep drawing of SUS304 stainless steel squares. Three stainless steel sheets with different thicknesses of 0.05 mm, 0.1 mm and 0.2 mm were treated by annealing processes at 1100 °C in which the holding times were varied in order to adjust the grain size. The sheets were used in the micro deep drawing processes for producing the square cups with 3 mm side length and 1.8 mm height. According to the design rules from references, the dimensions of the blank were determined to reduce the variation on the rim height of the square cup. The results showed that two peak values appeared on the load curves and the as-received sheet with the smallest grain size led to the largest load. Moreover, the cases of the as-received sheet with smaller grains had smoother surface textures than those of the annealed sheets with larger grains.

Abstract: This study investigated the effect of grain size on the cross wedge rolling of micro copper rod. Annealing techniques and equal channel angular extrusion were employed to refine the grains of copper, after which the treated copper was machined to prepare the cylindrical billets with 1 mm diameter for conducting experiments. The billets were rolled between a pair of the dies fixed in a developed cross wedge rolling system to form micro copper rods. The results show that the developed system was able to successfully produced micro copper rods. The grain refinement led to a higher hardness and thus a greater forming load. The rod with fine grans had a larger concave curvature radius of the end face. The grain size clearly influences the material flow in the cross wedge rolling processes of the micro copper rod.

Abstract: This study considered four types of punch, which were flat, conical, spherical and standardized punched, to investigate the effect of the punch shapes on the micro backward extrusion of brass. Brass (JIS C2600) materials were annealed at 500 °C, 600 °C, and 700 °C and resulted in different microstructures with grain sizes of 50 μm, 70 μm and 111 μm, respectively. The annealed brass materials were carefully machined as cylindrical billets with the same dimension of 1.1 mm in diameter and length. The billets were later used in the experiments of the micro backward extrusion to form cups with 1.1 mm diameter and 0.2 mm thickness. The experimental results show that the type of punch affecting load in an increasing order are spherical, standardized, conical and flat punches. The results also show that load increases with the punch speed, and reduces as grain size increases.

Abstract: Friction is one of the key factors affecting the metal forming process. If the friction effects of the process can be accurately modeled, it is able to improve simulations and help the research and development of the metal forming process. This study used cylindrical brass (JIS C2600) billets with the height and diameter of 1.1 mm for conducting the experiments of the micro combined forward and backward extrusion. The purpose of the study was to investigate the effects of punch surface topography on friction in the process. Four surface topography conditions for 0.8 mm diameter punches were prepared by grinding, polishing, grooving and micro electrical discharge machining processes. By comparing the ratio of the cup height to rod length of the extruded cups with the calibration curves established by simulations, the friction factor was estimated in a range from 0.3 to 0.6. The results showed that the punch surface topography significantly affect the friction in the extrusion process. The predicted loads using the estimated friction factors were in good agreement with the experimental results.

Abstract: Grain size and lubricating conditions influence material flow behaviours in micro metal forming processes. In this study, the brass (JIS C2700) tubes with 1.1 mm outer diameter and 0.5 mm inner diameter were treated by annealing at 400 °C, 500 °C and 600 °C to obtain various microstructures with the grain sizes of 20 μm, 34 μm and 80 μm, respectively. The treated tubes were machined and grounded to be 0.6 mm length specimens for the experiments of micro forward and backward hollow extrusion. Three lubricating conditions, which were dry, full and punch lubricated conditions, were carried out in the experiments. By comparing the upper cup height and rod length of the extruded specimens with the calibration curves established by finite element simulations, it is possible to estimate the friction factors in the processes. The results show that the dry conditions lead to stronger friction effects and thus larger friction factors. Moreover, the friction factor increased with grain size and stroke for all conditions.

Abstract: Micro metal forming is widely interested due to its potential in manufacturing micro parts with low costs and high production rate as the demands of compact devices have been increasing in many fields. This study uses micro ball punch deformation tests to investigate the effect of grain size on the formability of SUS 304 stainless steel sheets. The study employed annealing treatments to change the grain size of the sheets. By using three punches in different diameters in associated with three dies having an inner diameter of 2 mm and different die radii, it was able to perform micro bulging tests and obtain the bulging depths which were used to assess the formability of the sheets. The study shows that the grain size does affect the depth of the deformed dome in the ball punch deformation test at the micro scale.

Abstract: This study used the micro double cup extrusion of aluminum to investigate the effects of the surface roughness of workpiece and die on the tribological conditions involving mixed lubrication and plastic deformation. The aluminum billets with the diameter of 3 mm and the height of 4.5 mm in different surface roughnesses were prepared by grinding processes and used in the experiments under conditions of dry and molybdenum disulfide lubrication. To estimate the friction factors, the heights of the extruded cups were measured and compared with those predicted by finite element simulations using the law of constant shear stress. The results show that smaller workpiece surface roughness resulted in low and nearly constant friction in the early stage of the micro extrusion under the dry and lubricated conditions, which were reflected in the estimated friction factors. In the later stage of the extrusion processes, the workpiece surface finish became close to the one of the die for all tested conditions. The friction was clearly reduced in the dry condition but it became greater in the cases with the lubricated condition. The surface condition in the later stage of the micro extrusion process was believed to allow the lubricant to escape from the contact interface.

Abstract: The micro metal forming manufacturing system is essentially an ultra precision forming press that can manufacture various micro scale products from metal thin foil and bulk material. In this paper, the micro metal forming manufacturing system has been developed using a micro servo motor. A micro forming system has been developed in Japan with a micro press that is limited to the single forming process. However, a press with a multi forming process is needed and we set about performing research and development of assorted equipment, including investigation into micro deep drawing and the micro punching process. In order to achieve this goal, exploration into the micro forming process as related to the multi forming process must be preceded first. Material selection and analysis of the micro forming process are accomplished in this paper, and the basis research as to how to make the actual system is accomplished.