Computer controlled system for dieless drawing of tool steel bar

This paper describes the computer controlled processing of AISI-O1 steel rod by a dieless drawing method. Both the operation of a purposely built machine and the results of an experimental programme are described. The machine consisted of elements to provide a drawing force, a PID controlled band heater and an air/water cooling system to carry out the novel bar production process. The untreated material in bar form of initial diameter, 5 mm, was drawn in the temperature range of 600–750 °C at drawing velocities of 2.5–5 mm/min and with air-cooling provided in the pressure range 2–4 × 10⁵ Pa. The process ratio, i.e. the ratio of the drawing velocity to the heat/cooling device movement velocity was varied between 0.35 and 1.33. A novel load-control algorithm was executed to ensure a steady-state process and a high tolerance on the final drawn diameter.     

End formation of a round tube into a square section having small corner radii

Expansion and reduction are the two common end forming processes for tubes. In the tube end expansion process using a square punch, it is difficult to obtain a small corner radii due to the stretching of the tube around the punch corners. The wall thickness around the corners is small when compared to the side wall. Hence, a tube having a poor square look is formed. In this study, a 2-stage end expansion of a round tube end into a square section having an improved square look i.e. small corner radii and increase in wall thickness around corners is developed. In the 1st stage, the tube end is flared into a cone shape using a 30° conical die by axial compression. In the 2nd stage, the conical end of the tube is drawn through a taper square die using a conical bottom square punch, and a near square section is formed. A 15% ironing ratio is applied during the drawing process to flatten the side wall of the square. Experimental and FEM simulation were performed to evaluate and to verify the forming process. Although the height of the square section increases when the punch stroke at the 1st stage is increased. However, this increase is limited by the buckling of the pipe at the circular section of the thick blank tube. Since the conical end is drawn into a square section having different radial lengths, the bottom of the square section is uneven. The uneven bottom end is trimmed off in the later process. A square section having a maximum height of 32 mm after trimming is successfully obtained from the experiment for the punch stroke, S = 44 mm using an API 5 L tube.     

A novel superplastic dieless drawing using fracture phenomenon for fabrication of metal tubular microneedles

A new dieless drawing using fracture phenomenon is proposed to fabricate superplastic microneedles with ultrafine tip diameter. The fracture type of high ductility after superplastic deformation is used for fabrication of ultrafine tip. The tapered shape of the microneedles is controlled by varying the drawing speed. Shape control was realized using a fixed water-cooling coil for a needle length below 70 mm. Heating temperature and drawing acceleration affect the tip outer diameter. The microneedle with a tip outer diameter of about 50 μm is fabricated under optimized drawing conditions. The fabricated microneedles can be used for medical and biotechnology applications.     

Superplastic characteristic of Mn–Si–Cr alloyed ultrahigh carbon steel realized through a novel process

A novel process based on simple heat treatment was developed in order to explore the superplastic characteristic of Mn–Si–Cr alloyed ultrahigh carbon steel. After austenitizing at A₁ ? A_cm and slow cooling, a microstructure with superplastic “potential” was obtained. The microstructure with superplastic “potential”, mainly composed of martensite and spherical carbides, could transform to a fine (austenite + ferrite + spherical carbides) microstructure beneficial for superplasticity during subsequent warm deformation at just below A₁. The superplastic characteristic during warm deformation is as follows: flow stress stays at 30–50 MPa and the m value reaches 0.4–0.5 at a strain rate of 10^–4–2 × 10^?4 s^?1. The novel process has two advantages: ultrahigh strength (HRC52) and excellent ductility (the reduction of area ～45%) are ensured after superplastic forming without the need of supplementary heat treatment; internal stress in the microstructure obtained after superplastic forming can be avoided to a great extent.     

Magnetic pulse cladding of aluminum alloy on mild steel tube

Bi-metal tubes, which combine the advantageous properties of two different metals, are desirable in industries where corrosion resistance is important. A new cladding method named magnetic pulse cladding (MPC) was used to form bi-metal tubes. A cladding of mild steel tube by aluminum alloy (AA3003) was achieved. The effect of the geometry of the field shaper on cladding quality was investigated as well as other main process parameters, such as, feeding size, radial gap and discharge voltage. The mechanical property was evaluated by compression-shear test and a maximum strength of 79.2 MPa and an average of 29.7 MPa were attained to by the following process settings: profiled field shaper, feeding size of 12 mm, radial gap of 2.0 mm and discharge voltage of 15 kV. OM and SEM images show a smooth integral interface and a small wavy one. EDS mapping reveals the interfacial diffusion zone up to 50-μm wide. The results show that the proposed MPC process is able to form sound cladding bonds and could be applicable to a tubular clad component with a high axial length.     

Development of a reversible machining method for fabrication of microstructures by using micro-EDM

A new micromachining method for the fabrication of micro-metal structures by using micro-reversible electrical discharge machining (EDM) was investigated. The reversible machining combines the micro-EDM deposition process with the selective removal process, which provides the ability of depositing or removing metal material using the same micro-EDM machining system. From the discharge mechanism of micro-EDM, the process conditions of micro-EDM deposition were analyzed firstly. Using the brass and steel materials as a tool electrode, the micro-cylinders with 200 μm in diameter and height-to-diameter ratio of more than 5 were deposited on a high-speed steel surface. Then the machining procedure was transformed easily from deposition to selective removal process by switching the process conditions. Different removal strategies including micro-EDM drilling and micro-EDM milling were used in the machining. Micro-holes with 80 μm in diameter are drilled successfully in the radial direction of the deposited micro-steel cylinder. Also, a brass square column with 70 μm in side length and 750 μm in height, and a micro-cylinder with 135 μm in diameter and 1445 μm in height are obtained by using micro-EDM milling. Finally, the characteristics of the deposited material were analyzed. The results show that the material components of a deposited micro-cylinder are almost the same as those of the tool electrode, and the metallurgical bonding has been formed on the interface. In addition, the Vickers-hardness of 454Hv of the steel deposited material is higher when compared to the hardness of 200Hv of the raw steel electrode.     

Numerical simulation and experimentation of a novel micro scale laser high speed punching

A novel process technology for micro punching of thin sheet metals is presented in this paper. The laser induced shock waves act as the micro punch. The forming speed can be controlled by adjusting the laser energy. Micro holes of 250 μm in diameter were successfully punched on sheet metal of 10 μm in thickness by single pulse, and good edge quality was obtained. The micro die-opening is produced by electrical discharge machining (EDM) using the copper electrode of φ=220 μm. In the experiment, a sacrificial coating is used to generate high-pressure plasma under a laser pulse, so no signs of melting, burning, or ablation were observed on the workpiece. The novel process of micro scale laser high speed punching is also numerically studied. In addition, this method can be used to fabricate noncircular micro holes on thin sheet metals with noncircular micro die-openings. With further development, laser high speed punching may become an important micro punching technology, which is characterized by non-contact, low cost, and high efficiency.     

Punching of small hole of die-quenched steel sheets using local resistance heating

A punching process of a small hole in a die-quenched steel sheet having high strength using local resistance heating of a shearing zone was developed to decrease the punching load. Uniform temperature in the circular shearing zone of the hole was obtained by optimising heating conditions for a pair of rectangular electrodes. The punch load and the burnished surface area for the heating at 500 °C were about 1/3 smaller and 2 times larger than those for the cold punching, respectively, and the occurrence of delayed fracture around the punched hole was prevented by the heating above 500 °C.     

Effect of equal-channel angular pressing routes on high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy

The effect of equal-channel angular pressing (ECAP) route on the high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy was investigated. The 8-pass ECAPed specimens deformed via three different routes consisted of ultra-fine grains 0.5 μm in size, and contained a considerable amount of second-phase particles, which were fragmented and distributed in the matrix. In the torsion tests, the maximum shear stress significantly increased with increasing number of ECAP passes, while the maximum shear stress and fracture shear strain were lowest in the specimen deformed via route A among the three 8-pass ECAPed specimens. Observation of the deformed area beneath the fractured surface revealed the adiabatic shear bands of 100 μm in width in the specimen deformed via route A, which minimized the maximum shear stress and fracture shear strain, whereas they were hardly formed in the specimens deformed via route B or C. The formation of adiabatic shear bands was explained in terms of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity related to ECAP routes.     

Effect of crystalline anisotropy and forming conditions on thinning and rupturing in deep drawing of copper single crystal

Copper single crystal has excellent electrical properties and ductility, and it has a peculiar application in micro-manufacturing. In this paper, a specific mold was designed and made in order to conduct deep drawing of copper single crystal and evaluate the crystalline orientation effect to the local thinning and rupturing in the process. As a contrast, a finite element subroutine (VUMAT in ABAQUS) based on the crystal plasticity theory was developed to simulate the deep drawing process according to the experimental configurations. The results show that the (1 1 0) blank has better deep drawing performance than (0 0 1) blank; The crack of (0 0 1) blank originates at 〈1 0 0〉 orientation in the plane because 〈1 0 0〉 orientation has poor plasticity; friction is a crucial factor to the forming quality in a small scale deep drawing process; the simulations are in good agreement with the experiments, which also indicates the crystal plasticity model is very necessary to study the plastic forming of metallic material, especially the crystalline characteristics should be considered in the research.     

Large reduction die-less mandrel drawing of magnesium alloy micro-tubes

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.     

Superplastic deformation of a heat-resistant Al–Cu–Mg–Ag–Mn alloy

The superplastic behavior and deformation mechanism of a heat-resistant Al–Cu–Mg–Ag–Mn alloy prepared by ingot metallurgy was investigated by using optical microscopy, scanning electron microscopy and transmission electron microscopy. It is shown that the Al–Cu–Mg–Ag–Mn alloy shows good superplastic properties at temperatures higher than 450 °C and strain rates lower than 10^?2 s^?1. A maximum elongation-to-failure of 320% was observed at 500 °C and 5 × 10^?4 s^?1, where the corresponding strain rate sensitivity index m is 0.58 and the flow stress σ is 5.7 MPa. Microstructure studies revealed that the observed superplastic behavior resulted from severe grain elongation rather than grain boundary sliding. It is suggested that this phenomenon may provide a new concept for developing superplastic materials.     

The coupling influence of size effects and strain rates on the formability of austenitic stainless steel 304 foil

In order to understand the coupling influence of size effects and strain rates on the formability of the austenitic stainless steel 304 foils in micro scale, a series of micro scale limited dome height (LDH) tests were designed and conducted in three different speeds without lubricant on the annealed and as-received austenitic stainless steel 304 foils. In this study, a technique was developed to coat a layer of pure chromium (≈0.3 μm thick) on the foils and by using the etching process to make the micro square grids (50 μm × 50 μm) on the foils. Then, the foils were annealed at different temperatures for obtaining different microstructures. A set of the forming limit curves (FLC) of the foils were obtained and they can be used by industry right away for product design, process design and development, die design, and simulations, etc. Besides, the coupling influence of the size effects and the strain rates on the formability of the austenitic stainless steel 304 foils has been studied, observed and understood.     

Sintering of tungsten powder with and without tungsten carbide additive by field assisted sintering technology

Tungsten powder (0.6–0.9 μm) was sintered by field assisted sintering technology (FAST) at various processing conditions. The sample sintered with in-situ hydrogen reduction pretreatment and pulsed electric current during heating showed the lowest amount of oxygen. The maximum relative density achieved was 98.5%, which is from the sample sintered at 2000 °C, 85 MPa for 30 min. However, the corresponding sintered grain size was 22.2 μm. To minimize grain growth, nano tungsten carbide powder (0.1–0.2 μm) was used as sintering additive. By mixing 5 and 10 vol.% WC with W powder, densification was enhanced and finer grain size was obtained. Relative density above 99% with grain size around 3 μm was achieved in W–10 vol.% WC sintered at 1700 °C, 85 MPa, for 5 min.     

Effect of hot rolled grain size on the precipitation kinetics of nitrides in low carbon Al-killed steel

The precipitation of nitrides plays a general role in the industrial processing of deep drawing quality Al-killed low carbon steels. In this paper, the effect of hot rolled grain size on the precipitation of nitrides has been analysed. To evaluate the effect of grain size on the nitride precipitation kinetics, thermoelectric power based investigations have been performed on hot and cold rolled specimens.In the hot rolled state, the precipitation of nitrides occurs more intensively in the fine grain size microstructure (average grain size = 9 μm) than in the large grain size microstructure (average grain size = 23 μm) until the precipitated fraction of nitrides reaches about 70%. In the cold rolled state the effect of grain size is much less significant; probably the precipitation process occurs simultaneously at the grain boundaries and along dislocations. According to the simulation results, significant differences can be found between the precipitated fraction of nitrides in fine and large grain size sheets coiled in the temperature range 550–650 °C. In this interval, the precipitated nitride fraction is about two times larger in a fine grain microstructure (9 μm) than in sheets with 23 μm average grain size. The local position in the coil also affects significantly the precipitated fraction of nitrides. In the outer ring of the coil, less than 20% precipitated fraction is predicted in coiling temperature range 550–700 °C. However, in the middle ring of a hot rolled coil, the precipitated fraction changes from 5% to 85% with increasing coiling temperature from 550 to 700 °C.     

Improved properties of Ti6Al4V by means of nitrogen high temperature plasma based ion implantation

A stable heating source, providing steady temperatures in the range of 200 to more than 1000 °C, was used to perform high temperature plasma based ion implantation (PBII) on Ti6Al4V. The precise control of the heating of the samples in vacuum while performing PBII is accomplished by means of an efficient electron source, working independent of the conditions of the discharge.The electrons produced by a low work function (2.1 eV) barium, strontium and calcium oxide cathode help with the start-up of the discharge, with the increase of nitrogen ionization and heating of the samples. The large growth of the treated layer thickness was a result of the thermal diffusion of nitrogen, reaching up to 20 μm, in the total process time lasting only 100 min. Experiments were run by setting a constant substrate temperature during PBII to 800 °C but varying the pulse intensity and the duration of the process. Our results showed improvements of the mechanical and tribological properties, and also higher resistance to corrosion of the samples treated by high temperature PBII.     

The effect of microstructure and texture evolution on mechanical properties of low carbon steel in a non-circular drawing sequence

In this study, a new process sequence of non-circular and circular drawing is designed using finite element simulations and is proposed to produce strengthened wires in a simple continuous way for industrial applications. The developed non-circular drawing (NCD) sequence was experimentally applied to low carbon steel at room temperature. Mechanical properties, microstructure and texture evolution of the specimen processed by the newly proposed process and conventional wire drawing (WD) were investigated by tension test, electron backscattering diffraction (EBSD), and X-ray diffraction (XRD) for comparison. According to the present investigation, the specimen processed by the NCD sequence achieved 10.7% higher ultimate tensile strength (UTS) with slightly higher reduction of area at fracture than the one processed by the WD for the two-pass with the same area reductions. Furthermore, the UTS value (612 MPa) of the drawn wire by the two-pass NCD sequence was equivalent to the level of 602 MPa processed by the three-pass WD. From the EBSD results, the areal fraction of the low angle grain boundaries (1.12 μm⁻¹) of the specimen processed by the NCD was higher than that (0.78 μm⁻¹) of the specimen processed by the WD for the two-pass. The pole figures and ODFs of the specimen processed by the NCD sequence showed typical drawing and rolling textures. It is demonstrated that the non-circular drawing sequence could be beneficial in producing high-strength wires with comparable ductility through grain refinement according to the observations made in the present work.     

The effect of an electric current on the nanoindentation behavior of tin

Electrical–thermal–mechanical interactions determine the reliability and performance of microelectromechanical devices and systems. Using the nanoindentation technique the effect of an electric current on the indentation deformation of Sn strips was studied for an indentation load in the range 50–200 μN. During the indentation an electric current density in the range 993.05–4087.89 A cm^?2 was passed through the Sn strips, which introduced electrical–thermal–mechanical interactions. The experimental results showed that the reduced contact modulus decreased with increasing electric current density. For an electric current density less than 4087.89 A cm^?2 the decrease in the reduced contact modulus with increasing electric current density was mainly controlled by Joule heating due to an electrothermal interaction. The electrothermal interaction caused surface softening of the Sn strips. A simple relation is proposed to describe the dependence of the reduced contact modulus on the electric current density. The indentation hardness decreased with increasing indentation load, showing a normal indentation size effect. Using the relationship between indentation hardness and indentation depth from strain gradient plasticity theory we curve fitted the experimental data and found that both the indentation hardness at the limit of infinite depth and the characteristic length were dependent on the electric current density. Finite element analysis was performed to analyze the indentation deformation of a two-dimensional tin strip under the simultaneous action of an electric current. The simulation results showed that the contact modulus of tin decreased linearly with the square of the electric current density, qualitatively in accordance with experimental observations for an electric current density ? 2803.7 A cm^?2.     

Development of semi-dieless metal bellows forming process

A novel semi-dieless metal bellows forming process with local induction heating and axial compression without using any conventional dies is proposed. Firstly, the thickening of a tube is induced by local heating and axial compressive force. Secondly, the buckling of the tube occurs, producing a convoluted shape. The seamless tubes used are stainless steel SUS304 with an outer diameter of 5 mm and a thickness of 0.5 mm and 0.3 mm. The effects of compression ratio on the profiles of the bellows such as convolution height, pitch and thickness are investigated experimentally. It is found that convolution height can be controlled by compression ratio. Additionally, the mechanism of this process for fabrication of the metal bellows can be clarified by loading curve during processing. Furthermore, the validity of a two-step compression technique for improving convolution height and pitch is verified. The fundamental of the proposed technique can be confirmed as a basic key processing to fabricating metal bellows with various dimensions and small quantities.     

Superplastic behaviour of two extruded gamma TiAl(Mo,Si) materials

The superplastic properties of two intermetallic Ti–46.8Al–1.2(Mo,Si) and Ti–46Al–1.5(Mo,Si) (at.%) materials produced by arc melting and processed by hot extrusion in the temperature range between 1200 and 1250 °C were studied. The materials exhibited an equiaxic near γ microstructure with γ grains finer than 1 μm and some band like region of γ grains with a size ranging from 5 to 20 μm. The finer grained zone contained a volume fraction of about 12 vol% in the 46.8Al material and about 25 vol% in the 46Al material of finely dispersed α₂-Ti₃Al particles. Mechanical tests performed on both materials at strain rates ranging from 4.6×10⁻⁴ to 10⁻² s⁻¹ in the temperature range of 975–1050 °C showed strain rate sensitivity exponents of about 0.5 at most strain rates. A maximum elongation to failure of about 300% was obtained for the 46.8Al material while about 900% was recorded for the 46Al material at 1050 °C at a relatively high strain rate of 8×10⁻³ s⁻¹. This difference is attributed to the larger volume fraction of α₂-phase particles in the 46Al material that leads to a decrease of the number and size of band like regions of coarse γ grains. The microstructure in the fine-grained areas of both materials remains essentially constant during deformation. The mechanical behavior at high temperature of these superplastic materials can be explained by considering grain boundary sliding as the dominant deformation mechanism.