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Micro hydroforming is promising for fabricating complex micro components with a high aspect ratio. The aim of this study is to deepen the understanding of the size effects in micro hydroforming. Experimental work and FEM simulations of micro hydro-mechanical deep drawing (MHDD) were conducted. Voronoi model and real microstructure model were established. Real grain morphology can be considered in the real microstructure model. Local thinning in critical area of the drawn cups due to size effects can be predicted by the models. The simulation results agree with the MHDD test results.

In the fields of medicine, electronics and information, the demand for micro-scale parts has increased significantly. In the metal forming using foil materials, it is known that different deformation behavior from sheet material can be observed. To investigate the surface roughening and plastic strain distribution for metal foils under various biaxial tensile states, a compact Marciniak testing apparatus is newly developed. The developed apparatus is installed on an automatic XY stage of the laser confocal microscope and the deformed specimen can be observed in real time. To confirm the possibility of in-situ observation of surface roughening and plastic strain distribution, the tests such as measurement of strain paths, observation of fracture points and surface roughening is conducted for pure copper foils. As a result, the plastic strain distribution and local necking behavior of the copper foil under various biaxial tensile states including equi-biaxial and uniaxial tensile states can be observed. Moreover, in-situ observation of surface roughening behavior on three proportional loading paths could be conducted. Therefore, an effectivity of the developed apparatus for investigation of surface roughening and plastic strain distribution is found.

In this study, to improve dimensional accuracy of thermoformed products for carbon fiber reinforced thermoplastic (CFRTP) sheet, effects of sheet thickness, cooling rate on spring-in behavior are investigated by several thermal U-bending test. Matrix resin of the CFRTP is crystalline polyamide 6 (PA6) and plain woven textiles of carbon fiber is used for reinforcement. As a result, for thick sheet and slow cooling, spring-in angle is smaller. In addition, a revised spring-in prediction formula is proposed by considering crystallinity and cooling rate into coefficient of thermal expansion for precise spring-in prediction. The calculation results are compared with experimental. The proposed prediction formula has higher prediction quality than the conventional.

An uni-axial tensile test is one of the general methods to obtain plastic properties for estimating deformation behavior of materials in the simulation of practical metal forming process. Non-contact measurement is generally used because of determination of accurate plastic properties excepting for contact effects. In the conventional method, strain distribution of specimen sprayed with random pattern is measured by digital image correlation (DIC). However, sprayed treatments on the specimen surface is unsuitable under various testing conditions, for example an elevated temperature, micro scale, and large deformation. Thus, non-sprayed specimen is desirable under such test conditions. In this study, we propose perfectly non-contact strain distribution measurement by using DIC with laser speckle pattern generated on specimen surface by irradiation of laser source. True strain in the un-axial tensile test is measured by following methods (1) laser speckle pattern by DIC, and (2) conventional measurement method with tracking gage marks. As a result, strain level measured by DIC with laser speckle pattern has good agreement with that of conventional extensometer. Furthermore, the strain distribution can be measured successfully under uniform and non-uniform deformation during necking by proposed method. Thus, we can verify the validity of proposed measurement method for determination of plastic properties.

In this study, to improve the bulged shape accuracy in the former fuzzy adaptive controlled Y-shape tube hydroforming system with die-built-in sensors, a new highly-accurate contact sensor is developed and a new combination control scheme using two evaluation functions is introduced into the fuzzy control algorithm. The developed contact sensor consists of total 3 micro switches in orthogonal directions and enables setting into a counterpunch. The micro switches are aligned at 2 mm intervals on their central axis and the contact sensor has sensitivity of ± 1 mm. As a new combination control scheme, a new evaluation function was introduced into the previous input membership, and two types of evaluation functions at different locations, at the die-corner radius and the counterpunch head sites, are inputted into the input membership functions simultaneously and then the output membership functions are defuzzified, and finally the output control values can be determined. Compared the new in-process controlled Y-shape tube hydroforming system with the our previous one, the experimental result demonstrates a high filling at the bulged top head and higher shape accuracy and dimensional accuracy of bulged part.

The focus of this study is micro tube hydroforming (MTHF) for fabricating complex shaped tubular or three-dimensional hollow micro components, which is a scaled down technology of tube hydroforming. In our previous study, a new MTHF system with ultra-high pressure generator was developed and a T- and cross-shaped micro tube hydroforming of phosphorous-deoxidized copper tube with diameter of 500 µm and thickness of 100 µm was successful. In this study, a micro T-shaped hydroforming as well as a micro cross-shaped hydroforming are carried out to confirm influential factors on micro forming characteristics of MTHF. Lubrication condition, material property, formed shape and grain size are mainly considered as influential factors, and discussed.

Physical parameters such as microscopic roughness become very important in micro forming process due to increasing surface to volume ratio. As a very important phenomenon in metal forming process, friction size effects are becoming more attracting for researchers because traditional models are not reliable. In this study, the micro rolling deformation characterization has been investigated with SUS 304 stainless steel considering the effect of lubricant, and there exists a sticking area in the contact zone. The evolution of surface roughness and oil film thickness are analyzed. The foil thickness plays an important role in the tribological features of rolling. All the results have been verified experimentally via the desktop 2-Hi micro rolling mills.

The results of the experimental study on bending behaviour of AZ31 magnesium alloy extruded square tube under stretch press bending are presented. Cracking with buckling occurs at compressive side, but we can bend AZ31 tube at room temperature by means of applied axial tension during forming. The mechanism of bending behaviour of AZ31 magnesium alloy tube has been examined from the point of view of the position of neutral axis according to the mechanical properties under tension and compression and flow stress dependency on strain rate.

A novel rotary laser dieless drawing process for metal microtube with local heating using a laser irradiated from one direction is proposed. A metal microtube is rotated about a tensile axis by rotary stage with chucks for circumferential uniform temperature distribution. A tube of stainless steel SUS304 with an outer diameter of 0.5 mm and thickness of 0.13 mm is used in the experiments. The rotating effects on outer diameter variation and outer radius error are evaluated in laser dieless drawing. As a result, the outer diameter variation under a condition of non-rotation is higher than that under condition of rotation. Thus, the limit of stable drawing condition can be enhanced by rotating effect in laser dieless drawing. In addition, in case of laser heating irradiated from one direction under non-rotating, the deformation amount of irradiated side is larger than that of non-irradiated side in laser dieless drawing. Meanwhile, the microtube is drawn subequally under condition of rotation due to circumferential uniform temperature distribution. Thus, the distorted radial deformation can be restrained by rotating effect. From these results, the effectiveness of the proposed rotary laser dieless drawing for fabricating metal microtubes can be demonstrated experimentally.

© 2014 The Authors. Published by Elsevier Ltd. The formability of ultra-fine grained stainless steel is investigated in micro hydromechanical deep drawing. The materials used are ultra-fine grained stainless steel and SUS304-H with thickness of 20 and 50 m. The micro cups are successfully fabricated for the ultra-fine grained stainless steel but it cannot be fabricated for SUS304-H with thickness of 20 m. The fracture type of ultra-fine grained stainless steel foil is the shortage of tensile strength at plain strain state and does not change with a decrease of the thickness. In contrast, the fracture type of SUS304-H foil changes to the bending deformation with decreasing the thickness due to its low ductility. The ultra-fine grained metal foil is required to obtain the high formability and fabricate the sharp micro cups.

To develop an in-process fuzzy control system for tube hydroforming, a new die-embedded sensing system was developed and fuzzy control was used to determine adaptively suitable loading path. T-shape tube hydroforming experiments were conducted to confirm the validity of die-embedded system and in-process fuzzy control system. As a result, the validity of the die-embedded sensing system was confirmed. Besides, Evaluation functions were measured and the loading path was automatically determined in real-time. Furthermore, a T-shape tube was formed with a well wall thickness distribution. Consequently, it is confirmed that the developed in-process fuzzy control system is effective for T-shape tube hydroforming.

© 2014 The Authors. Published by Elsevier Ltd. A novel microforming process - Micro Cross Wedge Rolling has been proposed, which is very promising in producing micro stepped components. It is inevitable to confront with huge challenges in the development of micro cross wedge rolling technology. The influences of miniaturization, especially size effect, on process, accuracy control and product quality have to be studied. A micro cross wedge rolling testing rig has been designed and manufactured. Micro stepped components have been fabricated successfully by adopting flat wedge tools on this rig. The effects of surface roughness of tool, grain size in workpiece and cross sectional area reduction on surface morphology of rolled workpiece have been investigated.