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The microtube hydroforming process is a new type of micro forming technology developed based on the traditional tube hydroforming technology. The micro hollow components with complex shapes can be manufactured with metal micro tubes using micro tube hydroforming process. Although some researches have reported the relative research results such as the design of the experimental equipment etc., the microparts produced with the micro tube hydroforming process has the problems of the non-uniform of wall thickness, low bulge height as well as the high failure rate of the forming process. In the current study, FEM simulation of the micro cross shape tube hydroforming process of the micro SUS304 stainless steel tube with a commercial code was carried out. The availability of the FEM simulation model was verified by comparing the maximum bulge heights obtained in the test and simulation. The influence of the deformation parameters of the micro tube hydroforming process on the deformation behavior of the micro SUS304 stainless steel tube were studied by FEM simulation. The internal pressure loading path, the axial feed loading path and the friction coefficients of 0.05 were conducted. The results show that the more uniform thickness distribution and the bigger bulge height of the cross shape part were obtained with the optimized internal pressure loading path and the axial feed loading path.

Hydroforming processes of metal tubes and sheets are being widely applied in manufacturing because of the increasing demand for lightweight parts in sectors such as the automobile, aerospace, and ship-building industries [...]

A novel semi-dieless bellows forming process with a local heating technique and axial compression has been initiated for the past years. However, this technique requires a high difficulty in maintaining the output quality due to its sensitivity to the processing conditions. The product quality mainly depends on not only the temperature distribution in the radial and axial direction but also the compression ratio during the semi-dieless bellows process. A finite element model has clarified that a variety of temperature produced by unstable heating or cooling will promote an unstable bellows formation. An adjustment to the compression speed is adequate to compensate for the effect of the variety of temperatures in the bellows formation. Therefore, it is necessary to apply a real-time process for this process to obtain accurate and precise bellows. In this paper, we are proposing a vision-based fuzzy control to control bellows formation. Since semi-dieless bellows forming is an unsteady and complex deformation process, the application of image processing technology is suitable for sensing the process because of the possible wide analysis area afforded by applying the multi-sectional measuring. A vision sensing algorithm is developed to monitor the bellows height from the captured images. An adaptive fuzzy has been verified to control bellows formation from 5 mm stainless steel tube in to bellows profile up to 7 mm bellows height, processing speed up to 0.66 mm/s. The adaptive fuzzy control system is capable of appropriately adjusting the compression speed by evaluating the bellows formation progress. Appropriate compression speed paths guide bellows formation following deformation references. The results show that the bellows shape accuracy between target and experiment increase become 99.5% under given processing ranges.

Die-less drawing using wire mandrel was proposed aiming to develop the process to manufacture magnesium (Mg) alloy micro-tubes. The ratio of thickness to outer diameter of drawn tubes was controlled by changing drawing speed and feeding speed referring to the formula derived from “volume constancy principle”. The results were as follows. The attainable reduction limit was enhanced by raising heating temperature of mother tubes and the maximum cross-sectional reduction of 58.3% was obtained through a single pass drawing. Mg alloy micro-tubes with outer diameter of 3.35 mm and wall-thickness of 0.69 mm were fabricated through the optimized multi-pass drawing. Mg alloy micro-tubes developed in this study can be used for medical, medicinal, sanitary and chemical appliances.

Most of hexagonal close-packed (HCP) metals are lightweight metals. With the increasing application of light metal products, the production of light metal is increasingly attracting the attentions of researchers worldwide. To obtain a better understanding of the deformation mechanism of HCP metals (especially for Mg and its alloys), a new constitutive analysis was carried out based on previous research. In this study, combining the theories of strain gradient and continuum mechanics, the equal channel angular pressing process is analyzed and a HCP crystal plasticity constitutive model is developed especially for Mg and its alloys. The influence of elevated temperature on the deformation mechanism of the Mg alloy (slip and twin) is novelly introduced into a crystal plasticity constitutive model. The solution for the new developed constitutive model is established on the basis of the Lagrangian iterations and Newton Raphson simplification.

When tightening a large number of bolted joints, the calibrated wrench method is used. Since this method is indirect, the axial tension varies greatly in many cases. However, the calibrated wrench method is still widely used because of the simplicity of the tool and easy standardization. When the tightening torque and axial tension are considered to be two independent random variables, the axial tension (stress) is distributed within an elliptical confidence limit. Conventionally, it is thought that the shape of this distribution is a rhombus. Considering the permitted limit for a working load (stress) on a bolted joint, the elliptical variation has a larger margin to the yield point than that of a conventional rhombus. On the basis of this feature, we show in this paper that a higher tightening target torque and a higher axial tension can be set than before. By applying the elliptical confidence limit, one can obtain higher tightening torque and initial axial tension than the conventional values within a smaller range of variations. In this study, in the case of tightening a large number of bolted joints at factories and so forth, tightening reliability is considered as a problem associated with quality or process control and a probabilistic statistical method is investigated. Finally, we carry out analysis to establish the optimum tightening torque for bolted joints.

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.

A novel superplastic dieless drawing was performed for fabrication of ceramic tubes. The reduction in area of tube obtained through the drawing was controlled by changing feeding and drawing speeds. Some tested tubes showed extremely low drawing stress of 15 MPa and high value of strain rate sensitivity parameter of 0.42. Furthermore, the maximum reduction in area of 84% was accomplished through single pass drawing. Thus, the ceramic tubes showed a good superplasticity in the proposed process. The conclusion is that the proposed superplastic dieless drawing can be widely used for efficient fabrication of various ceramic tubes.

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.

Tooling feature size to minimum thickness becomes small in micro scale products and its ratio affects the deformation behavior in micro sheet forming significantly. In this study, the effect of this relative tooling feature size on drawing characteristics and effects to improve the drawability, such as friction holding effect, hydrodynamic lubrication effect and compression effect by blank edge radial pressure, in micro hydromechanical deep drawing (MHDD) are investigated using plasticity theory and numerical simulation. The results show that the micro drawing characteristics in MHDD can be improved by applying counter pressure. However, the required fluid pressures for friction holding and hydrodynamic lubrication effects increase as the relative punch diameter and/or die shoulder radius to thickness decrease, although the compression effect by radial pressure on the blank edge is independent of the relative tooling feature size.

Micro hydro deep drawing is a promising technology to fabricate micro metal products with complex 3D shapes. However, the size effects in the micro hydro deep drawing become considerable and significantly influence shape accuracy of drawn cups. In this study, a Voronoi micro scale simulation model was developed to consider the size effects of SUS304 foils. A surface layer model was additionally applied in the simulation to further explain the size effects. The micro hydro deep drawing experiments were conducted with annealed SUS304 foils and the drawn cups were examined. The wrinkling phenomenon was generally aggravated with the hydraulic pressure. Simulation results also show that the high hydraulic pressure does not improve the shape accuracy of the drawn cups as that in the normal scale hydro deep dawning process does. The simulation results are in accordance with the experimental results.

To refine the microstructure and improve the mechanical properties of metal tubes, a new concept of severe plastic deformation process of cyclic rotating bending (CRB) was newly introduced. The current study focused on the investigation of evolution of microstructure and mechanical properties of Al 6061 tube in the CRB process with different deformation conditions. For this purpose, the CRB processes were performed with different deformation temperatures, bending angles and deformation times. The tensile test and Vickers hardness test were employed to evaluate the tensile properties and micro-hardness of the tube, respectively. While the Optical Microscope and Scanning Electronic Microscope equipped with Electron Back-Scattered Diffraction were utilized for the microstructure characterizations. The results shows that the deformation temperature, bending angle and deformation time have the strong influences on the mechanical properties and microstructure of the tubes processed by the CRB process. As a result, the tube with an average grain size of about 55 µm, as well as ultimate tensile strength of 244 MPa and total elongation of 10.05% was successfully obtained with the optimized deformation condition of the CRB process with a temperature of 100 °C, bending angle of 174°, the rotation speed of 20 r/min, and deformation time of 5 min, respectively.

Micro forming is a promising technology and has drawn global attentions due to the urgent requirements on miniaturised products. Micro hydro deep drawing (MHDD) is a typical micro forming method and its products are widely applied in various fields, such as micro electro-mechanical systems (MEMS), medical and aerospace areas. However, tiny sizes of both products and tools are obstacles to investigate this novel technology. Therefore, finite element method (FEM) is adopted and modified to study the influence of processing parameters on micro drawing process and produced products. In this study, a normal hydro deep drawing model was developed, and then a voronoi blank model was generated to consider the size effects of materials. Additionally, a surface layer model was created based on the voronoi blank model. Therefore, the open and closed lubricant theory can be fulfilled and friction behaviour in MHDD can be considered. Subsequently, different processing parameters, such as hydraulic pressure and material inhomogeneity, were investigated. Simulation results indicate that a proper hydraulic pressure improves drawability and shape accuracy of the drawn cups. Moreover, material inhomogeneity affects the quality of drawn cups.

In this paper, the tribological behavior and its size effects in micro–hydromechanical deep drawing (MHDD) are theoretically and experimentally investigated. It is found that a required fluid pressure for hydrodynamic lubrication significantly increases with scaling down micro–scale due to a high sealablity at small relative punch diameter to minimum thickness. Moreover, the opposite tribological size effect from a conventional microforming appears in MHDD in which the fluid medium can be kept in open lubricant pockets (OLPs) by applying a fluid pressure and, the friction coefficient decreases as a specimen size decreases. Thus, MHDD can induce the hydrodynamic lubrication and lubrication in OLPs and improve the tribological behavior in microforming by applying the appropriate fluid pressure.

A heat assisted superplastic dieless drawing process that requires no dies or tools is applied to the drawing of a Zn-22Al and β titanium superplastic alloy for not only circular but also noncircular microtubes such as square, rectangular and noncircular multi core tubes having square inner and rectangular outer cross sections. As a result, the tendency has been to increase the limiting reduction in area with increasing strain rate sensitivity index m value. We successfully fabricate Zn-22Al alloy, AZ31 magnesium, β titanium circular microtubes with outer diameter of 191μm, 890μm and 180μm, respectively. Furthermore, a noncircular micro tube, which has inner square tubes with a 335μm side, and an outer rectangular tube of 533×923μm were fabricated successfully. During the dieless drawing process, the geometrical similarity law in cross section which the tube is drawn while maintaining its initial shape can be satisfied. The smooth surface can be obtained in case of superplastic dieless drawing process without contact situation with dies and tools. Consequently, it is found that the superplastic dieless drawing is effective for the fabrication of circular and noncircular multicore microtubes.

A novel superplastic dieless drawing technique with local heating and tensile deformation has been focused on for fabrication of zirconia ceramic tube. In this study, 3Y-TZP zirconia ceramic tube with outer diameter of 6mm and inner diameter of 4mm as a superplastic material is used experimentally. An apparatus of superplastic dieless drawing with rotary stage for circumferential uniform heating and acetylene burner for high temperature of 1700°C is developed. The superplastiac dieless drawing experiment is carried out to investigate the effect of the ratio of drawing speed to feeding speed on the flexible controllability of diameter after drawing process. As a result, the reduction in area after drawing process can be controlled by the ratio of drawing speed to feeding speed. In addition, a maximum reduction in area of 79.2% can be realized in this process. Consequently, the validity of developed apparatus of superplastic dieless drawing for Zirconia ceramic tube can be demonstrated.

A nonlinear friction coefficient model which considers contact pressure, sliding velocity and sliding length was developed to improve the accuracy of predictions of the formability of steel sheets. The effects of contact pressure and sliding velocity under mixed lubrication were estimated based on a friction test in which a long steel sheet was drawn between two dies. The effect of the sliding length under the condition of lack of lubricants was estimated in another friction test, in which a long tool bar was placed between steel sheets and drawn continuously at the same position on the sheets. The results of cup drawing experiments and a finite element (FE) forming analysis using the developed friction model demonstrated that the model improves the accuracy of predictions of the formability of steel sheets. Finally, the effect of press motion control with a servo press on formability improvement was estimated by using the nonlinear model.

© 2015 Elsevier B.V. All rights reserved. A micro-hydromechanical deep-drawing (MHDD) apparatus for manufacturing a micro-complex-shape components and increasing of drawn cup accuracy has been developed in this study. This apparatus with simple tooling structure and forming process can achieve high dimensional accuracy using servo press mechanics with a double-action type, one-stroke forming process without transferring and positioning, force control, and fine flow rate control of the pressure medium. The developed MHDD apparatus can prevent wrinkling by applying an appropriate constant gap and stably generate the counterpressure. Micro drawn cups of 0.8 mm diameter are successfully fabricated. Also, the effects of counterpressure on drawability and dimensional accuracy at the bottom of the cup are investigated for phosphor bronze, stainless-steel, and pure titanium foils with a thickness of 50 μm. The appropriate counterpressure applied in MHDD can eliminate wrinkling and reduce the frictional drawing force. It is concluded that the forming limit and dimensional accuracy can be improved by MHDD.

In this study, we investigate the effects of surface roughening and oxidation, which are dependent on the heating temperature, on the drawing limit in the dieless drawing process of SUS304 stainless steel microtubes. The microtubes have an outer diameter of 0.5 mm and a thickness of 0.13 mm. Dieless drawing apparatus with a chamber filled with argon gas to prevent oxidation is used in the experiments. It was found that the limiting reduction in area increases to a maximum value and then decreases with increasing heating temperature in both argon gas and air. An appropriate heating temperature range from 950 to 1100 °C with the maximum drawing limit is obtained from the dieless drawing experiment. In addition, the drawing limit in air is lower than that in argon gas at low temperatures of below 950 °C owing to oxidization. In contrast, the drawing limit in air at high temperatures of over 1100 °C is higher than that in argon gas, because the oxidation inhibits free surface roughening due to grain growth. Consequently, the drawing limit in dieless drawing strongly depends on the heating temperature. The roles of oxidation and surface roughening, which affect the drawing limit in the dieless drawing of microtubes, also vary widely depending on the heating temperature.

To generally describe the size effect in microforming operation under dry friction, which strongly depends on the contact state and geometrical/mechanical properties of the surface, the present study proposes a classification approach based on the theoretical scale-dependent model in microtribology. The proposed approach was applied to the practical problem of a scaled foil strip drawing test involving contact between a pair of compression tools made of WC–Co hard alloy and a phosphor bronze foil with a thickness of 20, 50, or 100 μm. From the results, it was clarified that the decreasing tendency of the total friction coefficient in the scaled foil strip drawing test was mainly due to the size effect of three-body deformation (plowing), which was promoted by the generation of wear particles. The applicability of the proposed method and the positioning in the transitional scale range of mesoscopic tribology in microforming operation were quantitatively demonstrated.

This paper deals with the identification of an empirical equation for predicting free surface roughness evolution. The equation has been proposed elsewhere, and, in contrast to widely used equations, assumes that the evolution of free surface roughness is controlled by two kinematic variables, the equivalent strain, and the logarithmic strain normal to the free surface. Therefore, an experimental program is designed to account for the effect of the mode of deformation on free surface roughness evolution. Thin sheets of aluminum alloy A5052-O and pure copper C1220P-O alloys are used to conduct the experimental program. In addition, numerical simulation is performed to calculate the evolution of free surface roughness under the same conditions. Comparison of experimental and numerical results shows that the accuracy of the numerical results is good enough. Then, numerical simulation is extended to the domain in which no experimental results are available. Discrete functions so found are fitted to polynomials. As a result, continuous functions that represent the empirical equation for predicting free surface roughness evolution for A5052-O and C1220P-O alloys are determined. These equations can be used in conjunction with solutions to boundary value problems in plasticity for predicting the evolution of free surface roughness in metal forming processes.

© 2016, Springer-Verlag France. This paper investigated the influences of temperature and grain size on the deformability of pure copper in micro compression process. Based on the dislocation theory, a constitutive model was proposed taking into account the influences of forming temperature, Hall-Petch relationship and surface layer model. Vacuum heat treatment was employed to obtain various grain sizes of cylindrical workpieces, and then laser heating method was applied to heat workpieces during microforming process. Finite element (FE) simulation was also performed, with simulated values agreed well with the experimental results in terms of metal flow stress. Both the FE simulated and experimental results indicate that forming temperature and grain size have a significant influence on the accuracy of the produced product shape and metal flow behaviour in microforming due to the inhomogeneity within the deformed material. The mechanical behaviour of the material is found to be more sensitive to forming temperature when the workpieces are constituted of fine grains.

A sophisticated servo press with the digital control has been developed and attracted attention in recent years. By utilizing its high function in-process, servo presses have a potential to enhance the forming limit and to improve quality and accuracy of product not only in sheet stamping but also in tube hydroforming processes. On the other hand, in-process control and adaptive process control technologies in metal forming processes using intelligent technique and soft computing have been investigated and developed previously. Nowadays we are in a good environment to realize further advanced adaptive in-process control in metal forming process. To further advance this technology, sensing system is essential element and it should be applied to feedback control optimally in their forming operation. This paper describes the current situation on advanced intelligent process control technology for sheet stamping and tube hydroforming processes on the basis of the research results by the author.

Transformation-induced plasticity aided seamless steel tube comprising of ferrite, bainite, and metastable austenite was processed through forging, piercing, cold-drawing, and two-stage heat treatment. T-shape hydroforming is a classic forming method for experimental research and practical production. The current work studied austenite-to-martensite transformation and microcrack initiation and propagation of the tube during T-shape hydroforming using electron backscattering diffraction, scanning electron microscopy, and transmission electron microscopy. The strain distribution in the bcc-phase and fcc-phase was studied by evaluating changes in the average local misorientation. Compared to the compressive stress, metastable austenite with similar strain surrounding or inside the grains transformed easier under tensile loading conditions. The inclusions were responsible for microcrack initiation. The propagation of the cracks is hindered by martensite/austenite constituent due to transformation induced plasticity effect. The volume fraction of untransformed retained austenite decreased with increase in strain implying transformation-induced plasticity effect.

We develop new drawing technologies of rotary laser dieless drawing for the fabrication of micro-tubes without the need for tools such as dies, plugs and mandrels. A rotary laser dieless drawing apparatus with local heating using a laser irradiated from one direction as the heating source has been focused on for the fabrication of micro-tubes. In this study, a dieless drawing with a semiconductor laser setup with power of 30W is designed and developed. A workpieces was 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 0.5mm and thickness of 0.13mm is used in the experiments. In this experiment, we verify the effectiveness of the developed rotary laser dieless drawing apparatus.