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A modeling of tribological size effects in micro deep drawing (MDD) and micro hydromechanical deep drawing (MHDD) is a main focus in this study. The inner and outer pockets in which the different friction coefficients can be applied at different lubrication conditions are considered on the blank surface. The ratio of the area of outer pockets to inner pockets is changed with the decrease in the size. The low friction coefficient at the outer pockets is assumed in MHDD by considering the lubrication effect of fluid medium. The numerical analysis is performed under six lubrication conditions. The analytical results of punch force-stroke curves are in good agreement with the experimental values. The friction force decreases in MHDD with the decrease in the size although it increases in MDD. The friction coefficient at die shoulder significantly influences the friction force due to high contact pressure in MHDD.

The demand for miniaturized parts and miniaturized semi-finished products is increasing. Metal forming processes cannot be simply scaled down to produce miniaturized micro parts and microforming processes have the capability of improving mass production and minimizing material waste. In this study, experimental and theoretical investigations on the micro rolling process have proven that the micro rolling deformation of thin strip is influenced by size effects from specimen sizeon flow stress and friction coefficient. The analytical and finite element (FE) models for describing the size effect related phenomena for SUS 304 stainless steel, such as the change of flow stress, friction and deformation behaviour, are proposed. The material surface constraint and the material deformation mode are critical in determination of material flow stress curve. The identified deformation and mechanics behaviours provide a basis for further exploration of the material deformation behaviour in plastic deformation of micro scale and the development of micro scale products via micro rolling.

The effect of thickness on surface roughening and onset of necking behavior was investigated experimentally. In addition, the effect of surface roughening and material properties on onset of necking behavior was discussed by using inhomogeneous FE simulation. Tensile test is conducted for pure aluminum, pure aluminum and pure titanium thin sheet with thickness of 0.05 and 0.5mm to observe the free surface roughening and necking behavior. Proposed inhomogeneous FE model can simulate the free surface roughening and necking behavior. The slope of ratio of surface roughness to thickness Rz/t is completely different between thickness of 0.5mm and 0.05. Therefore, the size effect on the ratio of surface roughness to thickness Rz/t can be observed. The magnitude relation between the increase in ratio of surface roughness to thickness and strain hardening exponent n value would affect the onset of localized necking behavior.

The paper presents the first step of research aimed at determining the specific form of a new empirical equation for free surface roughness evolution. In contrast to conventional empirical equations for free surface roughness evolution, the new equation introduces a dependence of the increment of roughness parameters on two kinematic variables. Nevertheless, it can be conveniently represented by a curve in appropriate space. The experimental method chosen is the process of plane strain bending of a sheet stressed by tensions applied to the ends. When the convex surface of the sheet is considered, one point of the aforementioned curve can be obtained. The theoretical part of the approach proposed consists of an analytic solution for an idealized process and simple geometric considerations.

Dieless drawing process was applied to small‐size non‐circular tubes. Deformation behavior of cross section of the fabricated tubes was investigated using finite element (FE) simulation. The FE simulation with coupled thermomechanical analysis using a commercial code; MSC MARC/Mentat was conducted considering strain rate sensitivity of the material tubes. In the calculation, the material properties were dealt with as a function of temperature in a special subroutine, whose constitutive equation considering strain rate sensitivity and strain hardening was used. Consequently, the effect of drawing condition on the deformation behavior of the tubes was clarified. Additionally, it was found that the geometrical similarity law in cross section was satisfied for small‐size non‐circular tubes. On the contrary, the geometrical similarity law in cross section is not satisfied in some cases that the length of heating coil is narrow. Therefore it is found that a certain level of deformation zone length on the basis of temperature distribution is necessary to satisfy the geometrical similarity law in cross section.

Dieless drawing is a unique deformation process without conventional dies, which can achieve a great reduction of wire and tube metals in single pass by means of local heating and cooling approach. In this study, for microtube forming, the dieless drawing process applying superplastic behavior was analyzed by finite element method (FEM) in order to clarify the effect of dieless tube drawing conditions such as tensile speed, moving speed of heating and cooling system, and material properties on deformation behavior of the tube. In the calculation, the material properties were dealt in a special subroutine, whose constitutive equation was defined as σ = Kenem, and was linked to the solver. A coupled thermo‐mechanical analysis was performed for the dieless tube drawing using the FEM. In the thermal analysis of dieless tube drawing, heat transfer was introduced to calculate the heat flux between heating coil and tube surface, and heat conduction in a tube. The influence of dieless tube drawing conditions on ...