Two-stage cold stamping of magnesium alloy cups having small corner radius

A two-stage cold stamping process for forming magnesium alloy cups having a small corner radius from commercial magnesium alloy sheets was developed. In the 1st stage, a cup having large corner radius was formed by deep drawing using a punch having large corner radius, and the corner radius of the cup was decreased by compressing the side wall in the 2nd stage. In the deep drawing of the 1st stage, fracture was prevented by decreasing the concentration of deformation with the punch having large corner radius. The magnesium alloy sheets were annealed at 500 °C to increase the cold formability. Circular and square cups having small corner radii were formed by the two-stage cold stamping. For the circular cup, the height of the cup was increased by ironing the side wall in the 1st stage. The radii of the bottom and side corners of the square cup were reduced by a rubber punch for applying pressure at these corners in the 2nd stage. It was found that comparatively shallow magnesium alloy square cups used as cases of laptop computers and mobile phones can be satisfactorily formed at room temperature without heating by the two-stage stamping.     

Eddy current analysis of mid-bore and corner cracks in bolt holes

Fatigue cracks are prone to develop around fasteners found in multi-layer aluminum structures on aging aircraft. Probability of Detection (POD) studies using eddy current techniques within the bolt holes contribute to risk assessments used in evaluating the serviceability of these aircraft. The signal response to corner and mid-bore cracks by eddy current testing using standard split-D differential probes has been examined. The data indicate that split-D probes are primarily sensitive to cracks at the corners of the Ds and that this gives rise to a double maximum for small mid-bore cracks as the corners pass over the crack. The double signal is not seen for corner cracks because the excitation coil, which is almost completely out of the hole, excites almost no eddy currents when the second corner of the D is over the crack. However, the eddy current response is more sensitive to corner cracks. The a_90/95 for corner cracks was measured to be 0.22 mm (length) compared to 0.34 mm (depth) and 0.62 mm (length) for mid-bore cracks. The enhanced detectability of corner cracks is attributed to the presence of the edge, which restricts passage of eddy currents around the crack.     

Development of a new process for producing deep square cups through conical dies

In this article, a new process for increasing the drawability of square cups has been developed. A circular blank is pushed by a flat-headed square punch through a conical die with a square aperture. The deformed blank conforms to the square shape of the die throat and finally a square cup is obtained. The developed technique has a simple tooling set in which the drawing process can be efficiently preformed in a single-acting stroke without using draw beads or blankholder. A commercial finite element simulation package, DYNAFORM, is used to investigate the developed setup in order to determine the optimum die cone angle. An experimental setup is built accordingly with a half cone angle of 18°. Brass alloy (67/33 Cu–Zn) and commercially pure aluminum (Al99.5w) sheets are used in the experimentations. The effects of the original blank thickness (t_o=1, 1.5, 2, 2.5, and 3 mm) and the orientation of the blank rolling direction (0°, 22.5°, 45°, and 67.5°) to the punch side on the limiting drawing ratio (LDR) and punch load are experimentally investigated. The present process successfully produces square cups with drawing ratios of 2.92 for brass and 2.74 for aluminum. The new process has shown superiority over the conventional methods through achieving high drawing ratio especially for thick sheets (2–3 mm). Comparison between experimental results and the available published work showed that the required punch force in the new process is significantly reduced while the LDR is increased.     

Evolution of springback and neutral layer of AZ31B magnesium alloy V-bending under warm forming conditions

The evolution of springback and neutral layer for AZ31B magnesium alloy sheet was investigated by V-bending tests at temperatures from 50 to 300 °C. Moreover, in order to perceive the influence of the punch radii on springback and offset of neutral layer, the tests with punch radii at 7.5, 8.1, 8.7 and 9.3 mm were conducted at 100 °C. The results show that the neutral layer shifts to the tension zone of the sheets. The coefficient of neutral layer (k-value) decreases with the increase of temperature and punch radii. This is mainly because of the asymmetry between the outer tension layer and inner compression layer during bending. The outer tension region is dominated by slip, while the inner compression region is dominated by twinning. With the increase of temperature, the asymmetry of tension–compression becomes weaker, and the offset of neutral layer decreases. The offset of neutral layer increases as punch radii decreases. The shift of neutral layer of AZ31B sheet results in the calculation of springback bigger than the reality.     

Fabrication of noncircular multicore microtubes by superplastic dieless drawing process

A superplastic dieless drawing process that requires no dies or tools is applied to the drawing of a Zn–22Al superplastic alloy for noncircular microtubes such as square, rectangular and noncircular multi core tubes having square inner and rectangular outer cross-sections. In this study, the effects of heating condition, such as heating length and the use or nonuse of cooling device, on deformation behavior are investigated. As a result, a square microtube with 0.58 mm side and a rectangular microtube of 0.75 mm × 1.3 mm were fabricated after 3-pass superplastic dieless drawing. In addition, the fundamental deformation behavior of noncircular tubes combined with square and rectangular tubes during the dieless drawing process has been clarified experimentally. The cross-sectional shape of the noncircular tubes after the superplastic dieless drawing process tends to be maintained on the basis of the similarity law in case of a wide heating length compared with a narrow heating length. Furthermore, a noncircular microtube, which has inner square tubes with a 335 μm side, and an outer rectangular tube of 533 μm × 923 μm were fabricated successfully after a 4-pass superplastic dieless drawing process. Consequently, it was found that the superplastic dieless drawing is effective for the fabrication of noncircular multicore microtubes.     

Plate forging of tailored blanks having local thickening for deep drawing of square cups

A plate forging process of tailored blanks having local thickening for the deep drawing of square cups was developed to improve the drawability. A sheet having uniform thickness was bent into a hat shape of two inclined portions, and then was compressed with a flat die under restraint of both edges to thicken the two inclined portions. The bending and compression were repeated after a right-angled rotation of the sheet for thickening in the perpendicular direction. The thickness of the rectangular ring portion equivalent to the bottom corner of the square cup was increased, particularly the thickening at the four corners of the rectangular ring undergoing large decrease in wall thickness in the deep drawing of square cups became double. The degree of thickening can be adjusted by controlling the punch stroke in the bending. By using the tailor blanks having local thickening, not only the decrease in wall thickness at the bottom corner of the square cup was prevented, but also the limiting drawing height of the cup without fracture was increased to 28.3 mm, whereas that for the uniform blank was 21.3 mm.     

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.     

Tailored die quenching of steel parts having strength distribution using bypass resistance heating in hot stamping

A tailored die quenching process of steel parts having a strength distribution using bypass resistance heating in hot stamping was developed. In the tailored die quenching process, zones requiring high strength in a quenchable steel sheet were heated, and then were quenched. In the bypass resistance heating, zones in contact with copper bypasses having a low resistance and large cross-sectional area were not heated due to the passage of the current though the copper bypasses. The bypass resistance heating was stable even for the heavy current in rapid heating of the steel sheets because of passage of current in one direction, and the electrical power loss was small. The hardenability for the bypass resistance heating was first examined by sandwiching a partially heated sheet between large steel blocks without deformation. Next, the tailored die quenching process using bypass resistance heating in the hat-shaped bending of the steel sheet was performed to form a part having high strength around the corners. A hat-shaped part having a tensile strength of approximately 1.5 GPa around the corners was formed, and the input energy and punching load in the bottom of the bent sheet were considerably smaller than those for whole heating.     

Texture evolution by shear on two planes during ECAP of a high-strength aluminum alloy

The evolution of texture was examined during equal-channel angular pressing (ECAP) of an Al–Zn–Mg–Cu alloy having a strong initial texture. An analysis of the local texture using electron backscatter diffraction demonstrates that shear occurs on two shear planes: the main shear plane (MSP) equivalent to the simple shear plane, and a secondary shear plane which is perpendicular to the MSP. Throughout most regions of the ECAP billet, the MSP is close to the intersection plane of the two channels but with a small (5°) deviation. Only the {1 1 1}〈1 1 0〉 and {0 0 1}〈1 1 0〉 shear systems were activated and there was no experimental evidence for the existence of other shear systems. In a small region at the bottom edge of the billet that passed through the zone of intersection of the channels, the observed textures were fully consistent with the rolling textures of Copper and Goss.     

Orientation dependence of nanoindentation pile-up patterns and of nanoindentation microtextures in copper single crystals

We present a study about the dependence of nanoindentation pile-up patterns and of microtextures on the crystallographic orientation using high purity copper single crystals. Experiments were conducted on a Hysitron nanoindentation setup using a conical indenter in order to avoid symmetries others than those of the crystal structure. Orientation measurements were conducted using a high resolution electron back-scatter diffraction technique for the automated acquisition of texture mappings around the indents. Simulations were carried out by means of a 3D elastic–viscoplastic crystal plasticity finite element method which takes full account of crystallographic slip and orientation changes during indentation. The experiments as well as the simulations show that the pile-up patterns on the surfaces of (0 0 1)-, (0 1 1)- and (1 1 1)-oriented single crystals have four-, two-, and sixfold symmetry, respectively. The different pile-up patterns can be explained in terms of the strong crystallographic anisotropy of the out-of-plane displacements around the indents. Pronounced accumulation of material entailing characteristic pile-up patterns occurs along the intersection vectors between the primary crystallographic slip planes and the indented surface planes.     

Bulk metallic glass tube casting

Tubular bulk metallic glass specimens were produced, using a custom-built combined arc-melting tilt-casting furnace. Zr55Cu30Al10Ni5 tubes with outer diameter of 25 mm and 0.8–3 mm wall thicknesses were cast, with both tilt and suction casting to ensure mold filling. Tilt casting was found to fill one side of the tube mold first, with the rest of the tube circumference filled subsequently by suction casting. Optimized casting parameters were required to fully fill the mold and ensure glass formation. Too small melt mass and too low arc power filled the mold only partially. However, too large melt mass and higher arc power which lead to the best mold filling also lead to partial crystallization. Variations in processing parameters were explored, until a glassy ring with 1.8 mm thickness was produced. Different sections of the as-cast ring were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and instrumented indentation to ensure amorphous microstructure. Atomic force microscopy (AFM) was used to compare the surface qualities of the first- and last-filled sections. These measurements confirmed the glassy structure of the cast ring, and that, the tilt cast tube section consistently showed better surface quality than the suction cast section. Optimized casting parameters are required to fully realize the potential of directly manufacturing complex shapes out of high-purity bulk metallic glasses by tilt casting.     

Optimization of metal foils surface finishing using vibration-assisted micro-forging

The present study focuses on optimizing metal foils surface finishing using vibration-assisted micro-forging. Different experimental parameters and specimens were used, and percentage of energy used for plastic deformation was calculated to find out the best conditions for surface finishing. The result shows that whether punch surface part with specimen or not is very important for the final surface roughness. The best vibration amplitude is larger than 2.47 μm and initial static stress is around 140 MPa. It is also found that face-centered cubic metal specimens with rougher surface and lower thickness are prone to gain a better surface.     

Enhancing formability in hydromechanical deep drawing process adding a shallow drawbead to the blank holder

In this paper, a new method was proposed in order to enhance the limiting drawing ratio (LDR) of AA5754-O in the hydromechanical deep drawing process (HDD). In the proposed method, a shallow drawbead was added to the blank holder to increase LDR so as to provide strain hardening of a large region on the flange of the sheet material in addition to pre-bulging process which affects particularly only the initial stage but not the later ongoing process. So the LDR of the AA5754-O was increased from 2.65 to 2.787 by enlarging the region of strain hardening in the flange and partially reducing wrinkling tendency due to occurred tensile stresses using the convenient pressure and blank holder force profiles. The importance levels and their convenient values for height of drawbead, pre-bulge height and pressure, surface roughness of the punch were determined with analysis of variance (ANOVA) is a statistical method. ANOVA analysis illustrated that adding a shallow drawbead to the blank holder is the most effective factor between the investigated factors for the HDD process. While the effects of the pre-bulging pressure and pre-bulging height were determined as quite small, the surface roughness of the punch was found unimportant compared to the effect of the shallow drawbead. The highest LDR value was obtained with 1 mm drawbead height, 5 mm pre-bulging height, 10 MPa pre-bulging pressure and 2.8 μm surface roughness of the punch.     

Gas forming of ultra-high strength steel hollow part using air filled into sealed tube and resistance heating

A new gas forming process of ultra-high strength steel hollow parts using air filled into sealed tubes and resistance heating was developed to omit the subsequent heat treatment. In this process, a sealed quenchable steel tube was rapidly resistance-heated to improve the formability. By applying die-quenching for holding at the bottom dead centre of a press, the formed part had very high strength, a hardness of 450 HV10 equivalents to a tensile strength of 1500 MPa. In addition, the dimensional accuracy of the formed part was improved by the increase in internal pressure for heating and compression of air filled into the sealed tube. To increase the hardness, the formed tube was cooled with air blowing during holding at the bottom dead centre and the corner of the die was optimised as to be in contact with the tube. The oxidation on the outer surface of the formed part was prevented by forming in a case filled with CO₂ gas.     

About the Al–Cu–Si isothermal section at 500 °C and the stability of the ɛ-Cu15Si4 phase

The 500 °C isothermal section of the Al–Cu–Si system has been determined in the whole composition range, with special attention to the Cu-rich corner. A number of Cu–Si binary alloys equilibrated at 500–780 °C have also been investigated.A ternary point compound at 1.5 at% Al and 21 at% Si has been identified. It has the same crystal structure of the binary phase previously reported as ?-Cu₁₅Si₄. This phase however is not stable in the binary system, at least between 500 and 780 °C, and it is stabilised by small amounts of impurities. The γ₁-(Al,Cu) phase dissolves about 11.5 at% Si and ternary solubility extends in the direction of a constant valence electron concentration. The binary κ-(Cu,Si) phase is stable in a ternary solubility range close to the (Cu) terminal solid solution.     

An innovative method to perform maskless plain waterjet milling for pocket generation: a case study in Ti-based superalloys

This paper presents an innovative methodology/jet path on which plain waterjet (PWJ) can generate pockets of good dimensional/geometrical definition (minimised under/over-erosion) while the proposed method leads to the avoidance of grit embedment on the target workpiece and the elimination of extra cost and time related to the use of mask.The novelty of the paper relies on the proposal of jet-path strategy that minimises the variations in jet dwell time by providing “continuous” relative movement during the jet-part interaction (through minimisation of accelerations/decelerations of the machine head) and by removing a controlled amount of material in a series of layers using special techniques. The proposed method is powerful in its approach from which it ensures (quasi)equal exposure time for each zone of material over which the jet passes, so that the jet path is “totally contained” within the form to be generated; hence, no masking is necessary to define the contour/shape.This approach has been employed for generating pockets on two Ti-based superalloys commonly used in aerospace industries, followed by dimensional, geometrical and surface quality analysis. The results proved that this approach can produce milled surfaces of straightness of the pocket bottom (<200 μm), tolerance on depth of cut per layer (<20 μm), tolerance on the radii at the bottom of the pockets (<100 μm), surface roughness (Ra=4–14 μm) and waviness (Wa=10–13 μm) characteristics in conditions of high surface integrity (no cracks, contaminations, etc.).     

Variation of temperature at the bottom surface of a hole during drilling and its effect on tool wear

The temperature at the bottom surface of a hole being drilled is measured by using an infrared-radiation pyrometer equipped with two optical fibers. One of the optical fibers is inserted into the oil hole of an internal coolant carbide drill and passes through the machine-tool spindle. This optical fiber is connected to another optical fiber at the end of the spindle. Infrared rays radiating from the bottom surface of the hole being drilled are accepted and transmitted to the pyrometer by the two optical fibers. Temperature increases as drilling progresses, and it increases considerably near the bottom surface of the workpiece. In case of a 10-mm-thick carbon–steel workpiece, temperature reaches 190, 250, and 340 °C at drilling depths of 6, 8, and 10 mm, respectively. To investigate the effect of the increase in temperature on drill wear, a series of 10-mm-deep blind holes are drilled in workpieces with thicknesses of 10 and 25 mm. Tool wear is greater when the drill cuts a hole at the bottom of a 10-mm workpiece than that when the drill cuts a hole at the mid-depth of a 25-mm workpiece. This indicates that the rapid increase in temperature near the bottom of the workpiece effects the progress of drill wear.     

A high-efficiency nondestructive method for remote detection and quantitative evaluation of pipe wall thinning using microwaves

We report an efficient nondestructive evaluation (NDE) method to measure the pipe wall thinning (PWT) remotely using microwaves. A microwave vector network analyzer (VNA) and a self-designed transmitting and receiving (T&R) coaxial-line sensor were employed in the experiment to generate microwave signals propagating in the pipe where the frequency was swept from 14.00 to 14.20 GHz. A brass pipe with inner diameter of 17.03 mm, 1.0 mm wall thickness, 2.0 m length, and connected, respectively, with 6 joints having the length of 17.0 mm and PWT from 0% to 60% of wall thickness was measured. By taking the pipe as a circular waveguide of microwave, after building up a resonance condition and then solving the resonance equations, the evaluation of PWT was realized. By comparing the evaluated results obtained using our suggested method with the nominal inner diameters of the joints, the maximum evaluation error is found to be less than 0.05 mm, which is less than 0.294% of the inner diameter of the pipe, which indicates that a high precision evaluation method is established.     

Polymer infrared photo-detector with high sensitivity up to 1100 nm

We reported a low band-gap conjugated polymer, poly[2,3-bis(4-(2-ethylhexyloxy)phenyl)-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine] (PDTTP), was studied for the near infrared (NIR) photo-detector application. PDTTP shows intense absorption in NIR wavelength (to 1000 nm) and the estimated optical and electrochemical band-gaps of PDTTP are quite small around 1.15 eV and 1.08 eV, respectively. The low band-gap and the extended long wavelength absorption originates from the introduction of alternating TP units when its parent polythieno[3,4-b]pyrazine shows excellent narrow band-gap properties. Therefore, the relatively low band-gap and intense absorption in long wavelength of PDTTP make itself a promising candidate for near-infrared photo-detector. The hole mobility of the PDTTP measured from the bottom contact field effect transistor is around 1.40 × 10^?3 cm²/V s with a on/off ratio of 2100. The photo-detector based on bulk hetero-junction PDTTP and (6,6)-phenyl-C61-butyric acid methyl ester blend (PCBM) has the incident photon-to-electron conversion efficiency 28.9% at 1000 nm (?5 V) and 6.2% at 1100 nm (?5 V). This photo-detector can be operated at a high-speed of 1 MHz. The experimental result suggests the potential applications of low band-gap conjugated polymers on near-infrared photo-detectors.     

Orientations of recrystallization nuclei developed in columnar-grained Ni at triple junctions and a high-angle grain boundary

A directionally solidified, high-purity nickel sample with a strong 〈0 0 1〉 fiber texture was cold rolled to 40% reduction. Electron backscattered diffraction (EBSD) was used to identify triple junctions (grain edges) before annealing the sample at 430 °C, after which further EBSD was performed to identify 17 recrystallization nuclei at the initially characterized triple junctions on the rolling plane. In addition, a longitudinal section was cut on which a further seven recrystallization nuclei were found and characterized. This characterization of all nuclei revealed that the majority of nuclei could be broadly associated with a 40° 〈1 1 1〉 misorientation to the matrix in which they formed, while a much lower percentage were found to have orientations as those of the local deformation substructure. However, a substantial fraction (around one-third) could not be associated with either of these types. Mechanisms for the formation of nuclei with new orientations are discussed, as is evidence of reorientation of material ahead of the recrystallization front.