Bending Step Research Articles

Adaptive multi-point flexible-bending technology for improving the quality of profile using discrete dies driven by snake-shaped motion mechanism

Based on the application of snake-spine-like structures, this paper proposes a roller-type multi-point flexible 3D profile bending process with snake-spine-like structures (Flexible stretch-bending with roller dies - driven by snake-like mechanism, FSBRD-S), and establishes a finite element model. Taking the L-shaped cross-section profile as the research object, different working modes and contact modes are defined to study their impact on crease defects during the vertical bending step, and the new structure is designed to improve the forming quality of the products' surface. The research results show that changing the contact mode leads to a change in the relative angle between the die and the billet. In the process of larger angle vertical bending, the FSBRD-S process can effectively reduce the crease defects generated by the traditional FSBRD process, especially in the area near the clamp. Furthermore, this article proposes the FSBRD-S shape-adjusting technology, which allows for adjustments to the FSBRD-S process based on actual needs, to obtain products with different surface qualities.

Protamine folds DNA into flowers and loop stacks

DNA in sperm undergoes an extreme compaction to almost crystalline packing levels. To produce this dense packing, DNA is dramatically reorganized in minutes by protamine proteins. Protamines are positively charged proteins that coat negatively charged DNA and fold it into a series of toroids. The exact mechanism for forming these ∼50-kbp toroids is unknown. Our goal is to study toroid formation by starting at the “bottom” with folding of short lengths of DNA that form loops and working “up” to more folded structures that occur on longer length scales. We previously measured folding of 200–300 bp of DNA into a loop. Here, we look at folding of intermediate DNA lengths (L = 639–3003 bp) that are 2–10 loops long. We observe two folded structures besides loops that we hypothesize are early intermediates in the toroid formation pathway. At low protamine concentrations (∼0.2 μM), we see that the DNA folds into flowers (structures with multiple loops that are positioned so they look like the petals of a flower). Folding at these concentrations condenses the DNA to 25% of its original length, takes seconds, and is made up of many small bending steps. At higher protamine concentrations (≥2 μM), we observe a second folded structure—the loop stack—where loops are stacked vertically one on top of another. These results lead us to propose a two-step process for folding at this length scale: 1) protamine binds to DNA, bending it into loops and flowers, and 2) flowers collapse into loop stacks. These results highlight how protamine uses a bind-and-bend mechanism to rapidly fold DNA, which may be why protamine can fold the entire sperm genome in minutes.

Systematic assessment of the flexibility of uracil damaged DNA

Uracil is a common DNA lesion which is recognized and removed by uracil DNA-glycosylase (UDG) as a part of the base excision repair pathway. Excision proceeds by base flipping, and UDG efficiency is thought to depend on the ease of deformability of the bases neighboring the lesion. We used molecular dynamics simulations to assess the flexibility of a large library of dsDNA strands, containing all tetranucleotide motifs with U:A, U:G, T:A or C:G base pairs. Our study demonstrates that uracil damaged DNA largely follows trends in flexibility of undamaged DNA. Measured bending persistence lengths, groove widths, step parameters and base flipping propensities demonstrate that uracil increases the flexibility of DNA, and that U:G base paired strands are more flexible than U:A strands. Certain sequence contexts are more deformable than others, with a key role for the 3′ base next to uracil. Flexibilities are large when this base is an A or G, and repressed for a C or T. A 5′ T adjacent to the uracil strongly promotes flexibility, but other 5′ bases are less influential. DNA bending is correlated to step deformations and base flipping, and bending aids flipping. Our study implies that the link between substrate flexibility and UDG efficiency is widely valid, helps explain why UDG prefers to bind U:G base paired strands, and suggests that the DNA bending angle of the UDG-substrate complex is optimal for base flipping. Communicated by Ramaswamy H. Sarma

Measuring DNA folding by the SARS-CoV-2 nucleocapsid protein.

The SARS-CoV-2 virus is a deadly virus responsible for COVID-19. Here we are interested in the mechanics of how the nucleocapsid protein (N-protein) in SARS-CoV-2 folds the viral RNA into the capsid. This process could be a target for antiviral research which looks to prevent further proliferation of the virus. Our goal is to understand the role that electrostatic interactions play in the folding of the negatively charged RNA by the positively charged N-protein. To isolate these interactions from specific interactions with the RNA bases or conformation, we measure N-protein folding single molecules of double-stranded DNA. We take structural images of the folding using an atomic force microscope (AFM) or look at real-time folding using tethered particle motion (TPM) assays. We hypothesize that N-proteins might fold double-stranded DNA using a method similar to positively charged protamine proteins which act to package the DNA in sperm cells. These protamine proteins “bind and bend” the DNA in multiple locations using discrete, long-lived (∼100 s), reversible bending steps. We observe similar folding characteristics for N-protein, but also see some important differences. We will report on progress toward this goal.

Adaptive sliding mode control of a magnetic levitation three-point bending device

This paper presents a non-contact three-point bending device based on magnetic levitation technology, in which a specimen can be bent while being levitated. As the levitated object needs to withstand an increasing bending load in levitated state, this requires the control system to have a strong robustness. Therefore, a centralized sliding mode controller (CSMC) was proposed for the levitation. Furthermore, based on CSMC, an adaptive centralized sliding mode controller with the bending load as scheduling variable (ACSMC), which is the novelty of this paper, were proposed to deal with the disturbance caused by the bending load. Simulation results demonstrated that ACSMC has good robustness to three typical bending loads, i.e., ramp load, sine load, step load. Finally, experiments were conducted and experiment results demonstrated that ACSMC allows the device to withstand ramp bending load, sine bending load and step bending load up to 50 N.

Residual stress analysis and its effect on springback for multi-step pressbrake bending

Pressbrake bending is a multi-step metal forming process and widely applied in the fields of aerospace, shipbuilding, and offshore industry. However, the bending residual stress that arise from the previous-pass bending step will affect the stress distribution of the next-pass bending step, and finally affect the springback after unloading, which results in the difficulty to guarantee the dimensional accuracy of the forming part. In this study, the residual stresses for multi-pass pressbrake forming and its influence on springback are systematically investigated. First, the analytical model for the residual stress of the bent specimen with initial curvature is deduced based on geometric relationship and elastic–plastic bending theory. Second, the calculation method of rigid body position redefine to simulate the multi-pass bending forming process is developed, and the numerical method is confirmed by comparison with experimental method. The analytical model to predict the residual stress is shown to be in close agreement with results from numerical method, demonstrating the validity of the analytical model. Finally, the impact of residual stress in single-pass and multi-pass bending forming on springback are discussed thoroughly. It is found that, as the number of forming passes increases, the equivalent plastic strain will increase to 9% of three-pass loading from 7.8% of one-pass loading, which explains the reason of increasing the number of bending passes can not only reduce springback, but also reduce the residual effect of bending forming.

Influence of Bus Bar Wiring Shape in PV Module on Surrounding Magnetic Field

Photovoltaic power generation systems have an electromagnetic interference problem caused by switching of power conditioning systems. As an example of this electromagnetic interference, interference to the AM radio band has been reported. It has also been reported that a bus bar, which is one of the internal wirings of a solar cell, is formed as an antenna. In this paper, the influence of the number of bending steps of the bus bar on the magnetic field was analyzed by the finite element method. As a result, it was found that when the bus bar has even-numbered stages, the magnetic flux density at the center is smaller than that of the odd-numbered stages.

Proprioceptive training in dance sport: effects of agility skills

The aim of this research is to determine the effects of proprioceptive training on the improvement of agility skills in dance sport fitness conditioning. Proprioceptive training is realized throughout tasks that include the establishing and maintaining various positions on balance boards of different dimensions, working surfaces and platforms. 38 male and female competitive dancers divided into an experimental and control groups. The experimental group took part in a proprioceptive training program over a period of 12 weeks (3 x 30 minutes per week). The control group (at the same time as the experimental) had regular sport dance training. At the beginning and at the end of the experiment, agility skills were measured by means of three different agility tests: Side steps, Figure '8' with bending and Agility in the air. Statistically significant differences among the groups in the final measurement (p= .00) generally show a positive effect of the proprioceptive training program on the improvement of agility skills with the experimental group, especially in tests Figure '8' with bending and Side steps. Such findings could encourage the use of proprioceptive training model in daily dance classes due to its potential to improve dancers' agility skills. Therefore, the use of a proprioceptive training model, as an innovative approach in individual and group dance fitness conditioning is recommended.

Model-Based Dynamic Calibration of a Multi-Actuator Gap Leveler for Heavy Plates

Abstract A novel method to calibrate the work rolls of a precision leveler for heavy plates is proposed. During the leveling process, a sequence of bending steps is imposed on the plate by the work rolls of the leveler to eliminate flatness defects. The respective positions of the rolls define the intensity of the consecutive bends. Any deviation from the desired roll position may result in a suboptimal leveling process. Thus, an exact control of the position of the work rolls is required. Due to backlash, wear, tolerances, and elastic deformation, the roll positions cannot be determined from nominal parameters and dimensions. Therefore, the machine has to be calibrated and properly adjusted to find suitable reference positions for control. During calibration, the structure is prestressed with a suitable test force and the signals of force and displacement sensors are recorded. As a result, reference points for future control inputs are obtained. A major drawback of a frequently used calibration method for levelers is that the work rolls of multi-actuator gap levelers cannot be properly calibrated. In practice, the work rolls are manually adjusted by the maintenance personnel of the machine. In this case, backlash may cause the loaded work rolls to deviate from their intended positions. Thus, a new method to calibrate the position of the individually actuated work rolls is developed and tested.

Selection of DNA Cleavage Sites by Topoisomerase II Results from Enzyme-Induced Flexibility of DNA

Topoisomerase II cleaves DNA at preferred sequences with different efficiencies; however, the mechanism of cleavage site selection is not known. Here we used single-molecule fluorescence assays that monitor several critical steps of DNA-topoisomerase II interactions, including binding/dissociation, bending/straightening, and cleavage/religation, and reveal that the cleavage site is selected mainly during the bending step. Furthermore, despite the sensitivity of the bending rate to the DNA sequence, it is not an intrinsic property of the DNA itself. Rather, it is determined by protein-DNA interactions.

Incremental Bending of Three-Dimensional Free Form Metal Plates Using Minimum Energy Principle and Model-Less Control

Bending 3D free form metal plates is a common process used in many heavy industries such as shipbuilding. The traditional method is the so-called line heating method, which is not only labor intensive but also inefficient and error-prone. This paper presents a new incremental bending method based on minimum energy principle and model-less control. First, the sheet metal is discretized into a number of strips connected through virtual springs. Next, by applying the minimum energy principle, the punching and supporting points are calculated for the strip. Then, the bended shape of the strip is computed based on the beam bending theory. This process is continued until the final shape is reached. To compensate the bending error, the computer vision-based model-less control is applied. The computer vision detects the bending error based on which additional bending steps are calculated. The new method is tested in a custom build incremental bending machine. Different metal plates are formed. For a metal plate of 1000 × 800 × 5 mm3, the average bending error is less than 3 mm. In comparison with the existing methods, the new method has a number of advantages, including simple, fast, and highly energy efficient.

Calculation tool and closed loop control for the JCO ® pipe forming process

Abstract In this paper, a new solution for the process planning and closed loop control of the JCO ® pipe forming process is presented. JCO ® pipe forming enables the production of open seam pipes out of steel plates by progressive bending (usually between 15 and 23 subsequent circumferential bending steps). Typical JCO ® pipes can be found in a diameter range from 457 to 1422 mm (18 to 56 inch) with wall thicknesses of up to 45 mm. These longitudinal-submerged arc-welded (LSAW) pipes are usually 12.2 or 18.3 m long. One crucial process parameter is the stroke for each single bending step depending on the required open seam pipe shape: With regard to subsequent process steps a perfect round shape is not always beneficial. Thus, the calculation software ShapeBase has been implemented into practice recently, taking into account the most important steps in the pipe production process chain. This fast software tool allows the process planning and optimisation of JCO ® plate forming to pipe. But due to variations in raw material (e.g. chemistry, yield point, wall thickness) even reliable theoretical calculations of process parameters can only be taken as initial machine values. To decrease further optimisation effort and increase the quality not only of the whole pipe lot but also of each single pipe, the above mentioned tool has been extended by an in-line measuring unit ShapeView and a real-time process control module ShapeControl.

Bending properties of different REBCO coated conductor tapes and Roebel cables at T = 77 K

Application of REBCO coated conductors in coils or cables involves deformation of the conductor in different modes, such as in-plane bending, out-of-plane bending and torsion. For example, the dipole magnet designs in the EuCARD-2 project require bending radii as low as 7.5 mm, inducing significant bending strain in the REBCO layer. In this paper, we investigate the effect of out-of-plane bending on the current-carrying properties of coated conductors from different manufacturers. The samples are manipulated by means of a Goldacker-type bending rig, which allows continuous bending at T = 77 K. By reversal to after each bending step, the reversible strain effect is separated from irreversible degradation. All tested conductors are found to tolerate compressive bending to a radius of 6 mm with less than 5% irreversible degradation of the critical current. The magnitude of the reversible strain effect shows a large variation among the samples. The effect of out-of-plane bending on Roebel cables is investigated as well, and the results are compared to the bending characteristic of single conductors. The results show no detrimental effect of the cable assembly on the bending properties within the constraints of the test.

Analysis of a quasi-three-point bending test for fabrics with friction and extensibility effect

This paper presents a theoretical bending model to investigate the quasi-three-point bending step of the comprehensive handle evaluation system for fabrics and yarns (CHES-FY). The effect of the friction and extensibility of fabrics on the bending step of the CHES-FY is discussed based on the theoretical bending model in three cases, and bending parameters, including maximum bending force, linear fitting slope and bending work, are featured from the bending force–displacement curves of each case. Comparisons of the theoretical and experimental results were also conducted to validate the model. The results revealed that the friction effect tended to enhance the bending parameters of the bending force–displacement curve of the bending step, and the effect of the friction could be remarkable at low bending rigidity of samples. However, the effect of the extensibility of samples was almost negligible for the bending test of wear fabrics, as the maximal relative error was less than 11.7% for fabrics where the tensile elastic constant was higher than 0.1 N/cm·%. This work can also provide a theoretical guidance for improving the measurement accuracy of the three-point bending test.

A Study on Making a Stable Loop Profile and Improving Bonding Time in Wire Bonding Process

Wire bonding is one of the most important processes in assembly of semiconductor. And the most competitive technology in wire bonding is making advanced loop profile. Therefore, as the growth of high-density and high-stacked die packages, it is essential to develop a highly lowed loop profile because wire bonding process is so sensitive in the semiconductor trend. Making a lowed loop profile is a key technology for today’s wire bonders. However, the conventional Folded Loop (FL) profile always accompanies many problems, such as critical faults due to un-stability at the neck of wire loop and long bonding time due to a lot of folding steps. These kinds of problems cause much of the un-efficient operation in the wire bonding. Therefore, we should develop an advanced loop profile to meet using more stable loop profile and applying speedy bonding time. The usual folded type loop profile can be developed by improving the shape of wire neck formation and reducing the kink steps for making lowed neck formation. In this paper, we propose a Very-Very Lowed Loop (VVLL) profile and it is the improved method to realize a fast and reliable loop profile in wire bonding process.Fig.1 shows that the result of the conventional FL profile and its 6-folding steps.Fig.2 describes 4-folding steps of the proposed VVLL profile and the bonding results.Fig.3 includes the critical problems of FL profile appeared at the loop neck position. Cracks are caused by 6-folding steps and direct touching of a capillary tool. In addition, the loop variation is also happened due to bouncing effects while realizing loop trajectory.Fig.4 depicts the advantages of VVLL. By decreasing the number of bending steps, it is possible to deconcentrate the stress and to reduce variation in the neck position of wire loop. Fig5 is shown how the one cycle bonding time is speedy by converting the folding method from FL to VVLL. It can reduce 2-steps of folding motion.To sum up, VVLL profile is significantly efficient to realize a fairly lowed and stable loop profile for state of the art high-tech semiconductor. REFERENCE Harman, George G. Wire bonding in microelectronics. McGraw-Hill, 2010 Brunner, Jon, Ivy Wei Qin, and Bob Chylak. "Advanced wire bond looping technology for emerging packages." Electronics Manufacturing Technology Symposium, 2004. Wang, Fuliang, Yun Chen, and Lei Han. "Modeling and experimental study of the kink formation process in wire bonding." Semiconductor Manufacturing, IEEE Transactions on 27.1 (2014): 51-59. Figure 1

Robust precision alignment algorithm for micro tube laser forming

Tube laser forming on a small diameter tube can be used as a high precision actuator to permanently align small (optical)components. Applications, such as the alignment of optical fibers to photonic integrated circuits, often require sub-micron alignment accuracy. Although the process causes significant scattering in bending angle and direction, this accuracy can be achieved by multiple bending steps of decreasing size once the target location is in proximity. In this paper an algorithm is proposed which, for each bending step, determines the best values of the main driving parameters; the axial laser spot position on the tube and the laser power. This algorithm is self-learning by using a statistical analysis of all previous bending steps. The algorithm is therefore robust for differences in for example the laser absorption between the tubes. A fully automated experimental micro tube bending setup has been developed using the proposed method in an algorithm to iteratively align an optical fiber to a virtual target with 0.1μm accuracy, using tubes with a diameter between 450μm and 700μm. For the best performing tube geometry, this required an average of 14.5 steps, where each step uses a single laser pulse with a spot position determined by the algorithm.

High precision optical fiber alignment using tube laser bending

In this paper, we present a method to align optical fibers within 0.2 μm of the optimal position, using tube laser bending and in situ measuring of the coupling efficiency. For near-UV wavelengths, passive alignment of the fibers with respect to the waveguides on photonic integrated circuit chips does not suffice. In prior research, it was shown that permanent position adjustments to an optical fiber by tube laser bending meets the accuracy requirements for this application. This iterative alignment can be done after any assembly steps. A method was developed previously that selects the optimal laser power and laser spot position on the tube, to minimize the number of iterations required to reach the target position. In this paper, that method is extended to the case where the absolute position of the fiber tip cannot be measured. By exploiting the thermal expansion motion at a relatively low laser power, the fiber tip can be moved without permanent deformation (only elastic strain) of the tube. An algorithm has been developed to search for the optimal fiber position, by actively measuring and maximizing the coupling efficiency. This search is performed before each bending step. Experiments have shown that it is possible to align the fiber with an accuracy of 0.2 μm using this approach.

Study on micro-patterning process of vertically aligned carbon nanotubes (VACNTs)

ABSTRACTVertically aligned carbon nanotubes (VACNTs) have drawn significant attention by the researchers because of their nanometric size and favorable material properties. Patterning of CNT forests in the micrometric domain is very important for their application in the area of microelectromechanical system (MEMS). For the first time this paper reports, detailed experimental investigation on a post growth μ-patterning process of VACNT forests. The micromechanical bending (M2B) process was locally applied at the targeted area in order to change the alignment of VACNT forests. Interestingly, the VACNT forest was transformed from typical black body absorber to reflective mirror as the M2B process was applied. Several parameters were identified that govern the resultant patterns such as rotational spindle speed, lateral bending speed, step size, tool morphology, and total depth of bend. Optimization of the parameters was carried out experimentally to obtain the best surface roughness and integrity of the microstructure. A minimum average surface roughness of Ra = 15 nm was achieved with 2000 rpm spindle speed, 1 mm/min bending speed and 1 µm step size.

Analysis of bending mechanism and spring-back characteristics in the offset Z-bending process

The Z-bending process has rarely been investigated because Z-shaped parts can be fabricated by applying two bending steps through V-bending processes. In recent years, the Z-bending process has been increasingly applied to reduce the number of processing steps and fabrication time. However, the number of studies on this process is still lacking, which means there is still difficulty with die and process designs when attempting to control the spring-back/spring-forward characteristics. In this study, to solve these problems, the offset Z-bending process was examined using the finite element method (FEM) and laboratory experiments. Based on the stress distribution analysis, the bending mechanism was investigated and clearly identified by analyzing changes in the stress distribution; the analysis showed that the theories of V-bending processes could not be used for the offset Z-bending process. This study also suggests that for the offset Z-bending process, in which the punch is moveable and the die is fixed, the amount of spring-back should not be equal to each other. In addition, the effects of the bend angle on the spring-back/spring-forward characteristics were investigated and clearly identified by analyzing the changes in the stress distribution. Based on the laboratory experiments, the FEM simulation results showed good agreement in terms of both the bend angles and bending forces.

Measurements of Chemical and Mechanical Properties of Rats and Mice Bones under Simulated Space‐Like Environment

Changes in elemental composition and mechanical properties of leg bones were determined following hind‐limb suspension (HLS) and irradiation of rats and mice. Tibia and Femur were bent with an applied force and corresponding elastic modulus determined. The bones were cross sectioned for elemental composition using Scanning Electron Microscopy with Energy Dispersive capabilities (EDX). The effect of microgravity on bones was evident after 4 days of suspension. There was a strong relationship between the compositional ratios of calcium, carbon, phosphorus and oxygen with the location on the leg. Two methods were used to measure mechanical strength of the bones; a LASER based bending setup (Cantilever) and a 3‐point bending setup with sensor to measure bending steps and stepping mechanism. Results showed that the femur bones had Young's modulus between 6 and 18 GN/m. For control groups, it was ~2.5 times larger than that for the HLS group. This clearly points to a less elastic nature of leg bones exposed to HLS. Also the trend of the stress versus strain graph (beyond the linear range) indicates a substantially lower breaking point for HLS leg bones. The results for tibia and femur provided similar conclusion. The elemental compositions in combination with mechanical properties indicated weakening of the bones under space‐like conditions of microgravity. These changes were even larger when radiation effects were taken into account. Supported by Arkansas Space Grant Consortium